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POSTCONF(5) POSTCONF(5)

NAME

postconf - Postfix configuration parameters

SYNOPSIS

postconf parameter ...

postconf -e "parameter=value" ...

DESCRIPTION

The Postfix main.cf configuration file specifies a small subset of all
the parameters that control the operation of the Postfix mail system.
Parameters not specified in main.cf are left at their default values.

The general format of the main.cf file is as follows:

· Each logical line has the form "parameter = value". Whitespace
around the "=" is ignored, as is whitespace at the end of a log-
ical line.

· Empty lines and whitespace-only lines are ignored, as are lines
whose first non-whitespace character is a `#'.

· A logical line starts with non-whitespace text. A line that
starts with whitespace continues a logical line.

· A parameter value may refer to other parameters.

· The expressions "$name", "${name}" or "$(name)" are
recursively replaced by the value of the named parameter.

· The expression "${name?value}" expands to "value" when
"$name" is non-empty. This form is supported with Postfix
version 2.2 and later.

· The expression "${name:value}" expands to "value" when
"$name" is empty. This form is supported with Postfix
version 2.2 and later.

· Specify "$$" to produce a single "$" character.

· When the same parameter is defined multiple times, only the last
instance is remembered.

· Otherwise, the order of main.cf parameter definitions does not
matter.

The remainder of this document is a description of all Postfix configu-
ration parameters. Default values are shown after the parameter name in
parentheses, and can be looked up with the "postconf -d" command.

Note: this is not an invitation to make changes to Postfix configura-
tion parameters. Unnecessary changes can impair the operation of the
mail system.

2bounce_notice_recipient (default: postmaster)
The recipient of undeliverable mail that cannot be returned to the
sender. This feature is enabled with the notify_classes parameter.

access_map_defer_code (default: 450)
The numerical Postfix SMTP server response code for an access(5) map
"defer" action, including "defer_if_permit" or "defer_if_reject". Prior
to Postfix 2.6, the response is hard-coded as "450".

Do not change this unless you have a complete understanding of RFC
2821.

This feature is available in Postfix 2.6 and later.

access_map_reject_code (default: 554)
The numerical Postfix SMTP server response code for an access(5) map
"reject" action.

Do not change this unless you have a complete understanding of RFC
2821.

address_verify_cache_cleanup_interval (default: 12h)
The amount of time between verify(8) address verification database
cleanup runs. This feature requires that the database supports the
"delete" and "sequence" operators. Specify a zero interval to disable
database cleanup.

After each database cleanup run, the verify(8) daemon logs the number
of entries that were retained and dropped. A cleanup run is logged as
"partial" when the daemon terminates early after "postfix reload",
"postfix stop", or no requests for $max_idle seconds.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.7.

address_verify_default_transport (default: $default_transport)
Overrides the default_transport parameter setting for address verifica-
tion probes.

This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)
Overrides the local_transport parameter setting for address verifica-
tion probes.

This feature is available in Postfix 2.1 and later.

address_verify_map (default: see postconf -d output)
Lookup table for persistent address verification status storage. The
table is maintained by the verify(8) service, and is opened before the
process releases privileges.

The lookup table is persistent by default (Postfix 2.7 and later).
Specify an empty table name to keep the information in volatile memory
which is lost after "postfix reload" or "postfix stop". This is the
default with Postfix version 2.6 and earlier.

Specify a location in a file system that will not fill up. If the data-
base becomes corrupted, the world comes to an end. To recover delete
(NOT: truncate) the file and do "postfix reload".

Postfix daemon processes do not use root privileges when opening this
file (Postfix 2.5 and later). The file must therefore be stored under
a Postfix-owned directory such as the data_directory. As a migration
aid, an attempt to open the file under a non-Postfix directory is redi-
rected to the Postfix-owned data_directory, and a warning is logged.

Examples:

address_verify_map = hash:/var/db/postfix/verify
address_verify_map = btree:/var/db/postfix/verify

This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)
Enable caching of failed address verification probe results. When this
feature is enabled, the cache may pollute quickly with garbage. When
this feature is disabled, Postfix will generate an address probe for
every lookup.

This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)
The time after which a failed probe expires from the address verifica-
tion cache.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)
The time after which a failed address verification probe needs to be
refreshed.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_poll_count (default: ${stress?1}${stress:3})
How many times to query the verify(8) service for the completion of an
address verification request in progress.

By default, the Postfix SMTP server polls the verify(8) service up to
three times under non-overload conditions, and only once when under
overload. With Postfix version 2.6 and earlier, the SMTP server always
polls the verify(8) service up to three times by default.

Specify 1 to implement a crude form of greylisting, that is, always
defer the first delivery request for a new address.

Examples:

# Postfix <= 2.6 default
address_verify_poll_count = 3
# Poor man's greylisting
address_verify_poll_count = 1

This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)
The delay between queries for the completion of an address verification
request in progress.

The default polling delay is 3 seconds.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)
The time after which a successful probe expires from the address veri-
fication cache.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)
The time after which a successful address verification probe needs to
be refreshed. The address verification status is not updated when the
probe fails (optimistic caching).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)
Overrides the relay_transport parameter setting for address verifica-
tion probes.

This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)
Overrides the relayhost parameter setting for address verification
probes. This information can be overruled with the transport(5) table.

This feature is available in Postfix 2.1 and later.

address_verify_sender (default: $double_bounce_sender)
The sender address to use in address verification probes; prior to
Postfix 2.5 the default was "postmaster". To avoid problems with
address probes that are sent in response to address probes, the Postfix
SMTP server excludes the probe sender address from all SMTPD access
blocks.

Specify an empty value (address_verify_sender =) or <> if you want to
use the null sender address. Beware, some sites reject mail from <>,
even though RFCs require that such addresses be accepted.

Examples:

address_verify_sender = <>
address_verify_sender = postmaster@my.domain

This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_default_transport_maps (default:
$sender_dependent_default_transport_maps)
Overrides the sender_dependent_default_transport_maps parameter setting
for address verification probes.

This feature is available in Postfix 2.7 and later.

address_verify_sender_dependent_relayhost_maps (default: $sender_depen-
dent_relayhost_maps)
Overrides the sender_dependent_relayhost_maps parameter setting for
address verification probes.

This feature is available in Postfix 2.3 and later.

address_verify_service_name (default: verify)
The name of the verify(8) address verification service. This service
maintains the status of sender and/or recipient address verification
probes, and generates probes on request by other Postfix processes.

address_verify_transport_maps (default: $transport_maps)
Overrides the transport_maps parameter setting for address verification
probes.

This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)
Overrides the virtual_transport parameter setting for address verifica-
tion probes.

This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)
The alias databases for local(8) delivery that are updated with
"newaliases" or with "sendmail -bi".

This is a separate configuration parameter because not all the tables
specified with $alias_maps have to be local files.

Examples:

alias_database = hash:/etc/aliases
alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)
The alias databases that are used for local(8) delivery. See aliases(5)
for syntax details.

The default list is system dependent. On systems with NIS, the default
is to search the local alias database, then the NIS alias database.

If you change the alias database, run "postalias /etc/aliases" (or
wherever your system stores the mail alias file), or simply run
"newaliases" to build the necessary DBM or DB file.

The local(8) delivery agent disallows regular expression substitution
of $1 etc. in alias_maps, because that would open a security hole.

The local(8) delivery agent will silently ignore requests to use the
proxymap(8) server within alias_maps. Instead it will open the table
directly. Before Postfix version 2.2, the local(8) delivery agent will
terminate with a fatal error.

Examples:

alias_maps = hash:/etc/aliases, nis:mail.aliases
alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)
Restrict local(8) mail delivery to external commands. The default is
to disallow delivery to "|command" in :include: files (see aliases(5)
for the text that defines this terminology).

Specify zero or more of: alias, forward or include, in order to allow
commands in aliases(5), .forward files or in :include: files, respec-
tively.

Example:

allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)
Restrict local(8) mail delivery to external files. The default is to
disallow "/file/name" destinations in :include: files (see aliases(5)
for the text that defines this terminology).

Specify zero or more of: alias, forward or include, in order to allow
"/file/name" destinations in aliases(5), .forward files and in
:include: files, respectively.

Example:

allow_mail_to_files = alias,forward,include

allow_min_user (default: no)
Allow a sender or recipient address to have `-' as the first character.
By default, this is not allowed, to avoid accidents with software that
passes email addresses via the command line. Such software would not be
able to distinguish a malicious address from a bona fide command-line
option. Although this can be prevented by inserting a "--" option ter-
minator into the command line, this is difficult to enforce consis-
tently and globally.

As of Postfix version 2.5, this feature is implemented by trivial-re-
write(8). With earlier versions this feature was implemented by
qmgr(8) and was limited to recipient addresses only.

allow_percent_hack (default: yes)
Enable the rewriting of the form "user%domain" to "user@domain". This
is enabled by default.

Note: with Postfix version 2.2, message header address rewriting hap-
pens only when one of the following conditions is true:

· The message is received with the Postfix sendmail(1) command,

· The message is received from a network client that matches
$local_header_rewrite_clients,

· The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty
value.

To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all".

Example:

allow_percent_hack = no

allow_untrusted_routing (default: no)
Forward mail with sender-specified routing (user[@%!]remote[@%!]site)
from untrusted clients to destinations matching $relay_domains.

By default, this feature is turned off. This closes a nasty open relay
loophole where a backup MX host can be tricked into forwarding junk
mail to a primary MX host which then spams it out to the world.

This parameter also controls if non-local addresses with sender-speci-
fied routing can match Postfix access tables. By default, such
addresses cannot match Postfix access tables, because the address is
ambiguous.

alternate_config_directories (default: empty)
A list of non-default Postfix configuration directories that may be
specified with "-c config_directory" on the command line, or via the
MAIL_CONFIG environment parameter.

This list must be specified in the default Postfix configuration direc-
tory, and is used by set-gid Postfix commands such as postqueue(1) and
postdrop(1).

always_add_missing_headers (default: no)
Always add (Resent-) From:, To:, Date: or Message-ID: headers when not
present. Postfix 2.6 and later add these headers only when clients
match the local_header_rewrite_clients parameter setting. Earlier
Postfix versions always add these headers; this may break DKIM signa-
tures that cover non-existent headers.

always_bcc (default: empty)
Optional address that receives a "blind carbon copy" of each message
that is received by the Postfix mail system.

Note: if mail to the BCC address bounces it will be returned to the
sender.

Note: automatic BCC recipients are produced only for new mail. To
avoid mailer loops, automatic BCC recipients are not generated for mail
that Postfix forwards internally, nor for mail that Postfix generates
itself.

anvil_rate_time_unit (default: 60s)
The time unit over which client connection rates and other rates are
calculated.

This feature is implemented by the anvil(8) service which is available
in Postfix version 2.2 and later.

The default interval is relatively short. Because of the high frequency
of updates, the anvil(8) server uses volatile memory only. Thus, infor-
mation is lost whenever the process terminates.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

anvil_status_update_time (default: 600s)
How frequently the anvil(8) connection and rate limiting server logs
peak usage information.

This feature is available in Postfix 2.2 and later.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

append_at_myorigin (default: yes)
With locally submitted mail, append the string "@$myorigin" to mail
addresses without domain information. With remotely submitted mail,
append the string "@$remote_header_rewrite_domain" instead.

Note 1: this feature is enabled by default and must not be turned off.
Postfix does not support domain-less addresses.

Note 2: with Postfix version 2.2, message header address rewriting hap-
pens only when one of the following conditions is true:

· The message is received with the Postfix sendmail(1) command,

· The message is received from a network client that matches
$local_header_rewrite_clients,

· The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty
value.

To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all".

append_dot_mydomain (default: yes)
With locally submitted mail, append the string ".$mydomain" to
addresses that have no ".domain" information. With remotely submitted
mail, append the string ".$remote_header_rewrite_domain" instead.

Note 1: this feature is enabled by default. If disabled, users will not
be able to send mail to "user@partialdomainname" but will have to spec-
ify full domain names instead.

Note 2: with Postfix version 2.2, message header address rewriting hap-
pens only when one of the following conditions is true:

· The message is received with the Postfix sendmail(1) command,

· The message is received from a network client that matches
$local_header_rewrite_clients,

· The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty
value.

To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all".

application_event_drain_time (default: 100s)
How long the postkick(1) command waits for a request to enter the
server's input buffer before giving up.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)
List of users who are authorized to flush the queue.

By default, all users are allowed to flush the queue. Access is always
granted if the invoking user is the super-user or the $mail_owner user.
Otherwise, the real UID of the process is looked up in the system pass-
word file, and access is granted only if the corresponding login name
is on the access list. The username "unknown" is used for processes
whose real UID is not found in the password file.

Specify a list of user names, "/file/name" or "type:table" patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A "/file/name" pattern
is replaced by its contents; a "type:table" lookup table is matched
when a name matches a lookup key (the lookup result is ignored). Con-
tinue long lines by starting the next line with whitespace. Specify
"!pattern" to exclude a name from the list. The form "!/file/name" is
supported only in Postfix version 2.4 and later.

This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)
List of users who are authorized to view the queue.

By default, all users are allowed to view the queue. Access is always
granted if the invoking user is the super-user or the $mail_owner user.
Otherwise, the real UID of the process is looked up in the system pass-
word file, and access is granted only if the corresponding login name
is on the access list. The username "unknown" is used for processes
whose real UID is not found in the password file.

Specify a list of user names, "/file/name" or "type:table" patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A "/file/name" pattern
is replaced by its contents; a "type:table" lookup table is matched
when a name matches a lookup key (the lookup result is ignored). Con-
tinue long lines by starting the next line with whitespace. Specify
"!pattern" to exclude a user name from the list. The form "!/file/name"
is supported only in Postfix version 2.4 and later.

This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)
List of users who are authorized to submit mail with the sendmail(1)
command (and with the privileged postdrop(1) helper command).

By default, all users are allowed to submit mail. Otherwise, the real
UID of the process is looked up in the system password file, and access
is granted only if the corresponding login name is on the access list.
The username "unknown" is used for processes whose real UID is not
found in the password file. To deny mail submission access to all users
specify an empty list.

Specify a list of user names, "/file/name" or "type:table" patterns,
separated by commas and/or whitespace. The list is matched left to
right, and the search stops on the first match. A "/file/name" pattern
is replaced by its contents; a "type:table" lookup table is matched
when a name matches a lookup key (the lookup result is ignored). Con-
tinue long lines by starting the next line with whitespace. Specify
"!pattern" to exclude a user name from the list. The form "!/file/name"
is supported only in Postfix version 2.4 and later.

Example:

authorized_submit_users = !www, static:all

This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)
What SMTP clients are allowed to specify the XVERP command. This com-
mand requests that mail be delivered one recipient at a time with a per
recipient return address.

By default, only trusted clients are allowed to specify XVERP.

This parameter was introduced with Postfix version 1.1. Postfix ver-
sion 2.1 renamed this parameter to smtpd_authorized_verp_clients and
changed the default to none.

Specify a list of network/netmask patterns, separated by commas and/or
whitespace. The mask specifies the number of bits in the network part
of a host address. You can also specify hostnames or .domain names (the
initial dot causes the domain to match any name below it),
"/file/name" or "type:table" patterns. A "/file/name" pattern is
replaced by its contents; a "type:table" lookup table is matched when a
table entry matches a lookup string (the lookup result is ignored).
Continue long lines by starting the next line with whitespace. Specify
"!pattern" to exclude an address or network block from the list. The
form "!/file/name" is supported only in Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside [] in
the authorized_verp_clients value, and in files specified with
"/file/name". IP version 6 addresses contain the ":" character, and
would otherwise be confused with a "type:table" pattern.

backwards_bounce_logfile_compatibility (default: yes)
Produce additional bounce(8) logfile records that can be read by Post-
fix versions before 2.0. The current and more extensible "name = value"
format is needed in order to implement more sophisticated functional-
ity.

This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)
The per-table I/O buffer size for programs that create Berkeley DB hash
or btree tables. Specify a byte count.

This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)
The per-table I/O buffer size for programs that read Berkeley DB hash
or btree tables. Specify a byte count.

This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)
Where the Postfix SMTP client should deliver mail when it detects a
"mail loops back to myself" error condition. This happens when the
local MTA is the best SMTP mail exchanger for a destination not listed
in $mydestination, $inet_interfaces, $proxy_interfaces, $vir-
tual_alias_domains, or $virtual_mailbox_domains. By default, the Post-
fix SMTP client returns such mail as undeliverable.

Specify, for example, "best_mx_transport = local" to pass the mail from
the Postfix SMTP client to the local(8) delivery agent. You can specify
any message delivery "transport" or "transport:nexthop" that is defined
in the master.cf file. See the transport(5) manual page for the syntax
and meaning of "transport" or "transport:nexthop".

However, this feature is expensive because it ties up a Postfix SMTP
client process while the local(8) delivery agent is doing its work. It
is more efficient (for Postfix) to list all hosted domains in a table
or database.

biff (default: yes)
Whether or not to use the local biff service. This service sends "new
mail" notifications to users who have requested new mail notification
with the UNIX command "biff y".

For compatibility reasons this feature is on by default. On systems
with lots of interactive users, the biff service can be a performance
drain. Specify "biff = no" in main.cf to disable.

body_checks (default: empty)
Optional lookup tables for content inspection as specified in the
body_checks(5) manual page.

Note: with Postfix versions before 2.0, these rules inspect all content
after the primary message headers.

body_checks_size_limit (default: 51200)
How much text in a message body segment (or attachment, if you prefer
to use that term) is subjected to body_checks inspection. The amount
of text is limited to avoid scanning huge attachments.

This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)
The recipient of postmaster notifications with the message headers of
mail that Postfix did not deliver and of SMTP conversation transcripts
of mail that Postfix did not receive. This feature is enabled with the
notify_classes parameter.

bounce_queue_lifetime (default: 5d)
The maximal time a bounce message is queued before it is considered
undeliverable. By default, this is the same as the queue life time for
regular mail.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

Specify 0 when mail delivery should be tried only once.

This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)
The name of the bounce(8) service. This service maintains a record of
failed delivery attempts and generates non-delivery notifications.

This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)
The maximal amount of original message text that is sent in a non-
delivery notification. Specify a byte count. A message is returned as
either message/rfc822 (the complete original) or as text/rfc822-headers
(the headers only). With Postfix version 2.4 and earlier, a message is
always returned as message/rfc822 and is truncated when it exceeds the
size limit.

Notes:

· If you increase this limit, then you should increase the
mime_nesting_limit value proportionally.

· Be careful when making changes. Excessively large values will
result in the loss of non-delivery notifications, when a bounce
message size exceeds a local or remote MTA's message size limit.

bounce_template_file (default: empty)
Pathname of a configuration file with bounce message templates. These
override the built-in templates of delivery status notification (DSN)
messages for undeliverable mail, for delayed mail, successful delivery,
or delivery verification. The bounce(5) manual page describes how to
edit and test template files.

Template message body text may contain $name references to Postfix con-
figuration parameters. The result of $name expansion can be previewed
with "postconf -b file_name" before the file is placed into the Postfix
configuration directory.

This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)
Enable inter-operability with SMTP clients that implement an obsolete
version of the AUTH command (RFC 4954). Examples of such clients are
MicroSoft Outlook Express version 4 and MicroSoft Exchange version 5.0.

Specify "broken_sasl_auth_clients = yes" to have Postfix advertise AUTH
support in a non-standard way.

canonical_classes (default: envelope_sender, envelope_recipient,
header_sender, header_recipient)
What addresses are subject to canonical_maps address mapping. By
default, canonical_maps address mapping is applied to envelope sender
and recipient addresses, and to header sender and header recipient
addresses.

Specify one or more of: envelope_sender, envelope_recipient,
header_sender, header_recipient

This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)
Optional address mapping lookup tables for message headers and
envelopes. The mapping is applied to both sender and recipient
addresses, in both envelopes and in headers, as controlled with the
canonical_classes parameter. This is typically used to clean up dirty
addresses from legacy mail systems, or to replace login names by First-
name.Lastname. The table format and lookups are documented in canoni-
cal(5). For an overview of Postfix address manipulations see the
ADDRESS_REWRITING_README document.

If you use this feature, run "postmap /etc/postfix/canonical" to build
the necessary DBM or DB file after every change. The changes will
become visible after a minute or so. Use "postfix reload" to eliminate
the delay.

Note: with Postfix version 2.2, message header address mapping happens
only when message header address rewriting is enabled:

· The message is received with the Postfix sendmail(1) command,

· The message is received from a network client that matches
$local_header_rewrite_clients,

· The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty
value.

To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all".

Examples:

canonical_maps = dbm:/etc/postfix/canonical
canonical_maps = hash:/etc/postfix/canonical

cleanup_service_name (default: cleanup)
The name of the cleanup(8) service. This service rewrites addresses
into the standard form, and performs canonical(5) address mapping and
virtual(5) aliasing.

This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)
The location of all postfix administrative commands.

command_execution_directory (default: empty)
The local(8) delivery agent working directory for delivery to external
command. Failure to change directory causes the delivery to be
deferred.

The following $name expansions are done on command_execution_directory
before the directory is changed. Expansion happens in the context of
the delivery request. The result of $name expansion is filtered with
the character set that is specified with the execution_directory_expan-
sion_filter parameter.

$user The recipient's username.

$shell The recipient's login shell pathname.

$home The recipient's home directory.

$recipient
The full recipient address.

$extension
The optional recipient address extension.

$domain
The recipient domain.

$local The entire recipient localpart.

$recipient_delimiter
The system-wide recipient address extension delimiter.

${name?value}
Expands to value when $name is non-empty.

${name:value}
Expands to value when $name is empty.

Instead of $name you can also specify ${name} or $(name).

This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)
Restrict the characters that the local(8) delivery agent allows in
$name expansions of $mailbox_command and $command_execution_directory.
Characters outside the allowed set are replaced by underscores.

command_time_limit (default: 1000s)
Time limit for delivery to external commands. This limit is used by the
local(8) delivery agent, and is the default time limit for delivery by
the pipe(8) delivery agent.

Note: if you set this time limit to a large value you must update the
global ipc_timeout parameter as well.

config_directory (default: see postconf -d output)
The default location of the Postfix main.cf and master.cf configuration
files. This can be overruled via the following mechanisms:

· The MAIL_CONFIG environment variable (daemon processes and com-
mands).

· The "-c" command-line option (commands only).

With Postfix command that run with set-gid privileges, a config_direc-
tory override requires either root privileges, or it requires that the
directory is listed with the alternate_config_directories parameter in
the default main.cf file.

connection_cache_protocol_timeout (default: 5s)
Time limit for connection cache connect, send or receive operations.
The time limit is enforced in the client.

This feature is available in Postfix 2.3 and later.

connection_cache_service_name (default: scache)
The name of the scache(8) connection cache service. This service main-
tains a limited pool of cached sessions.

This feature is available in Postfix 2.2 and later.

connection_cache_status_update_time (default: 600s)
How frequently the scache(8) server logs usage statistics with connec-
tion cache hit and miss rates for logical destinations and for physical
endpoints.

connection_cache_ttl_limit (default: 2s)
The maximal time-to-live value that the scache(8) connection cache
server allows. Requests that specify a larger TTL will be stored with
the maximum allowed TTL. The purpose of this additional control is to
protect the infrastructure against careless people. The cache TTL is
already bounded by $max_idle.

content_filter (default: empty)
After the message is queued, send the entire message to the specified
transport:destination. The transport name specifies the first field of
a mail delivery agent definition in master.cf; the syntax of the next-
hop destination is described in the manual page of the corresponding
delivery agent. More information about external content filters is in
the Postfix FILTER_README file.

Notes:

· This setting has lower precedence than a FILTER action that is
specified in an access(5), header_checks(5) or body_checks(5)
table.

· The meaning of an empty next-hop filter destination is version
dependent. Postfix 2.7 and later will use the recipient domain;
earlier versions will use $myhostname. Specify "default_fil-
ter_nexthop = $myhostname" for compatibility with Postfix 2.6 or
earlier, or specify a content_filter value with an explicit
next-hop destination.

cyrus_sasl_config_path (default: empty)
Search path for Cyrus SASL application configuration files, currently
used only to locate the $smtpd_sasl_path.conf file. Specify zero or
more directories separated by a colon character, or an empty value to
use Cyrus SASL's built-in search path.

This feature is available in Postfix 2.5 and later when compiled with
Cyrus SASL 2.1.22 or later.

daemon_directory (default: see postconf -d output)
The directory with Postfix support programs and daemon programs. These
should not be invoked directly by humans. The directory must be owned
by root.

daemon_timeout (default: 18000s)
How much time a Postfix daemon process may take to handle a request
before it is terminated by a built-in watchdog timer.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

data_directory (default: see postconf -d output)
The directory with Postfix-writable data files (for example: caches,
pseudo-random numbers). This directory must be owned by the mail_owner
account, and must not be shared with non-Postfix software.

This feature is available in Postfix 2.5 and later.

debug_peer_level (default: 2)
The increment in verbose logging level when a remote client or server
matches a pattern in the debug_peer_list parameter.

debug_peer_list (default: empty)
Optional list of remote client or server hostname or network address
patterns that cause the verbose logging level to increase by the amount
specified in $debug_peer_level.

Specify domain names, network/netmask patterns, "/file/name" patterns
or "type:table" lookup tables. The right-hand side result from
"type:table" lookups is ignored.

Pattern matching of domain names is controlled by the par-
ent_domain_matches_subdomains parameter.

Examples:

debug_peer_list = 127.0.0.1
debug_peer_list = example.com

debugger_command (default: empty)
The external command to execute when a Postfix daemon program is
invoked with the -D option.

Use "command .. & sleep 5" so that the debugger can attach before the
process marches on. If you use an X-based debugger, be sure to set up
your XAUTHORITY environment variable before starting Postfix.

Example:

debugger_command =
PATH=/usr/bin:/usr/X11R6/bin
ddd $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)
The default database type for use in newaliases(1), postalias(1) and
postmap(1) commands. On many UNIX systems the default type is either
dbm or hash. The default setting is frozen when the Postfix system is
built.

Examples:

default_database_type = hash
default_database_type = dbm

default_delivery_slot_cost (default: 5)
How often the Postfix queue manager's scheduler is allowed to preempt
delivery of one message with another.

Each transport maintains a so-called "available delivery slot counter"
for each message. One message can be preempted by another one when the
other message can be delivered using no more delivery slots (i.e.,
invocations of delivery agents) than the current message counter has
accumulated (or will eventually accumulate - see about slot loans
below). This parameter controls how often is the counter incremented -
it happens after each default_delivery_slot_cost recipients have been
delivered.

The cost of 0 is used to disable the preempting scheduling completely.
The minimum value the scheduling algorithm can use is 2 - use it if you
want to maximize the message throughput rate. Although there is no max-
imum, it doesn't make much sense to use values above say 50.

The only reason why the value of 2 is not the default is the way this
parameter affects the delivery of mailing-list mail. In the worst case,
their delivery can take somewhere between (cost+1/cost) and
(cost/cost-1) times more than if the preemptive scheduler was disabled.
The default value of 5 turns out to provide reasonable message response
times while making sure the mailing-list deliveries are not extended by
more than 20-25 percent even in the worst case.

Use transport_delivery_slot_cost to specify a transport-specific over-
ride, where transport is the master.cf name of the message delivery
transport.

Examples:

default_delivery_slot_cost = 0
default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)
The default value for transport-specific _delivery_slot_discount set-
tings.

This parameter speeds up the moment when a message preemption can hap-
pen. Instead of waiting until the full amount of delivery slots
required is available, the preemption can happen when transport_deliv-
ery_slot_discount percent of the required amount plus transport_deliv-
ery_slot_loan still remains to be accumulated. Note that the full
amount will still have to be accumulated before another preemption can
take place later.

Use transport_delivery_slot_discount to specify a transport-specific
override, where transport is the master.cf name of the message delivery
transport.

default_delivery_slot_loan (default: 3)
The default value for transport-specific _delivery_slot_loan settings.

Use transport_delivery_slot_loan to specify a transport-specific over-
ride, where transport is the master.cf name of the message delivery
transport.

default_destination_concurrency_failed_cohort_limit (default: 1)
How many pseudo-cohorts must suffer connection or handshake failure
before a specific destination is considered unavailable (and further
delivery is suspended). Specify zero to disable this feature. A desti-
nation's pseudo-cohort failure count is reset each time a delivery com-
pletes without connection or handshake failure for that specific desti-
nation.

A pseudo-cohort is the number of deliveries equal to a destination's
delivery concurrency.

Use transport_destination_concurrency_failed_cohort_limit to specify a
transport-specific override, where transport is the master.cf name of
the message delivery transport.

This feature is available in Postfix 2.5. The default setting is com-
patible with earlier Postfix versions.

default_destination_concurrency_limit (default: 20)
The default maximal number of parallel deliveries to the same destina-
tion. This is the default limit for delivery via the lmtp(8), pipe(8),
smtp(8) and virtual(8) delivery agents. With per-destination recipient
limit > 1, a destination is a domain, otherwise it is a recipient.

Use transport_destination_concurrency_limit to specify a transport-spe-
cific override, where transport is the master.cf name of the message
delivery transport.

default_destination_concurrency_negative_feedback (default: 1)
The per-destination amount of delivery concurrency negative feedback,
after a delivery completes with a connection or handshake failure.
Feedback values are in the range 0..1 inclusive. With negative feed-
back, concurrency is decremented at the beginning of a sequence of
length 1/feedback. This is unlike positive feedback, where concurrency
is incremented at the end of a sequence of length 1/feedback.

As of Postfix version 2.5, negative feedback cannot reduce delivery
concurrency to zero. Instead, a destination is marked dead (further
delivery suspended) after the failed pseudo-cohort count reaches
$default_destination_concurrency_failed_cohort_limit (or $trans-
port_destination_concurrency_failed_cohort_limit). To make the sched-
uler completely immune to connection or handshake failures, specify a
zero feedback value and a zero failed pseudo-cohort limit.

Specify one of the following forms:

number

number / number
Constant feedback. The value must be in the range 0..1 inclu-
sive. The default setting of "1" is compatible with Postfix
versions before 2.5, where a destination's delivery concurrency
is throttled down to zero (and further delivery suspended) after
a single failed pseudo-cohort.

number / concurrency
Variable feedback of "number / (delivery concurrency)". The
number must be in the range 0..1 inclusive. With number equal to
"1", a destination's delivery concurrency is decremented by 1
after each failed pseudo-cohort.

A pseudo-cohort is the number of deliveries equal to a destination's
delivery concurrency.

Use transport_destination_concurrency_negative_feedback to specify a
transport-specific override, where transport is the master.cf name of
the message delivery transport.

This feature is available in Postfix 2.5. The default setting is com-
patible with earlier Postfix versions.

default_destination_concurrency_positive_feedback (default: 1)
The per-destination amount of delivery concurrency positive feedback,
after a delivery completes without connection or handshake failure.
Feedback values are in the range 0..1 inclusive. The concurrency
increases until it reaches the per-destination maximal concurrency
limit. With positive feedback, concurrency is incremented at the end of
a sequence with length 1/feedback. This is unlike negative feedback,
where concurrency is decremented at the start of a sequence of length
1/feedback.

Specify one of the following forms:

number

number / number
Constant feedback. The value must be in the range 0..1 inclu-
sive. The default setting of "1" is compatible with Postfix ver-
sions before 2.5, where a destination's delivery concurrency
doubles after each successful pseudo-cohort.

A pseudo-cohort is the number of deliveries equal to a destination's
delivery concurrency.

Use transport_destination_concurrency_positive_feedback to specify a
transport-specific override, where transport is the master.cf name of
the message delivery transport.

This feature is available in Postfix 2.5 and later.

default_destination_rate_delay (default: 0s)
The default amount of delay that is inserted between individual deliv-
eries to the same destination; with per-destination recipient limit >
1, a destination is a domain, otherwise it is a recipient.

To enable the delay, specify a non-zero time value (an integral value
plus an optional one-letter suffix that specifies the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

NOTE: the delay is enforced by the queue manager. The delay timer state
does not survive "postfix reload" or "postfix stop".

Use transport_destination_rate_delay to specify a transport-specific
override, where transport is the master.cf name of the message delivery
transport.

This feature is available in Postfix 2.5 and later.

default_destination_recipient_limit (default: 50)
The default maximal number of recipients per message delivery. This is
the default limit for delivery via the lmtp(8), pipe(8), smtp(8) and
virtual(8) delivery agents.

Setting this parameter to a value of 1 changes the meaning of the cor-
responding per-destination concurrency limit from concurrency per
domain into concurrency per recipient.

Use transport_destination_recipient_limit to specify a transport-spe-
cific override, where transport is the master.cf name of the message
delivery transport.

default_extra_recipient_limit (default: 1000)
The default value for the extra per-transport limit imposed on the num-
ber of in-memory recipients. This extra recipient space is reserved
for the cases when the Postfix queue manager's scheduler preempts one
message with another and suddenly needs some extra recipients slots for
the chosen message in order to avoid performance degradation.

Use transport_extra_recipient_limit to specify a transport-specific
override, where transport is the master.cf name of the message delivery
transport.

default_filter_nexthop (default: empty)
When a content_filter or FILTER request specifies no explicit next-hop
destination, use $default_filter_nexthop instead; when that value is
empty, use the domain in the recipient address. Specify "default_fil-
ter_nexthop = $myhostname" for compatibility with Postfix version 2.6
and earlier, or specify an explicit next-hop destination with each con-
tent_filter value or FILTER action.

This feature is available in Postfix 2.7 and later.

default_minimum_delivery_slots (default: 3)
How many recipients a message must have in order to invoke the Postfix
queue manager's scheduling algorithm at all. Messages which would
never accumulate at least this many delivery slots (subject to slot
cost parameter as well) are never preempted.

Use transport_minimum_delivery_slots to specify a transport-specific
override, where transport is the master.cf name of the message delivery
transport.

default_privs (default: nobody)
The default rights used by the local(8) delivery agent for delivery to
external file or command. These rights are used when delivery is
requested from an aliases(5) file that is owned by root, or when deliv-
ery is done on behalf of root. DO NOT SPECIFY A PRIVILEGED USER OR THE
POSTFIX OWNER.

default_process_limit (default: 100)
The default maximal number of Postfix child processes that provide a
given service. This limit can be overruled for specific services in the
master.cf file.

default_rbl_reply (default: see postconf -d output)
The default SMTP server response template for a request that is
rejected by an RBL-based restriction. This template can be overruled by
specific entries in the optional rbl_reply_maps lookup table.

This feature is available in Postfix 2.0 and later.

The template is subject to exactly one level of $name substitution:

$client
The client hostname and IP address, formatted as name[address].

$client_address
The client IP address.

$client_name
The client hostname or "unknown". See
reject_unknown_client_hostname for more details.

$reverse_client_name
The client hostname from address->name lookup, or "unknown".
See reject_unknown_reverse_client_hostname for more details.

$helo_name
The hostname given in HELO or EHLO command or empty string.

$rbl_class
The blacklisted entity type: Client host, Helo command, Sender
address, or Recipient address.

$rbl_code
The numerical SMTP response code, as specified with the
maps_rbl_reject_code configuration parameter. Note: The numeri-
cal SMTP response code is required, and must appear at the start
of the reply. With Postfix version 2.3 and later this informa-
tion may be followed by an RFC 3463 enhanced status code.

$rbl_domain
The RBL domain where $rbl_what is blacklisted.

$rbl_reason
The reason why $rbl_what is blacklisted, or an empty string.

$rbl_what
The entity that is blacklisted (an IP address, a hostname, a
domain name, or an email address whose domain was blacklisted).

$recipient
The recipient address or <> in case of the null address.

$recipient_domain
The recipient domain or empty string.

$recipient_name
The recipient address localpart or <> in case of null address.

$sender
The sender address or <> in case of the null address.

$sender_domain
The sender domain or empty string.

$sender_name
The sender address localpart or <> in case of the null address.

${name?text}
Expands to `text' if $name is not empty.

${name:text}
Expands to `text' if $name is empty.

Instead of $name you can also specify ${name} or $(name).

Note: when an enhanced status code is specified in an RBL reply tem-
plate, it is subject to modification. The following transformations
are needed when the same RBL reply template is used for client, helo,
sender, or recipient access restrictions.

· When rejecting a sender address, the Postfix SMTP server will
transform a recipient DSN status (e.g., 4.1.1-4.1.6) into the
corresponding sender DSN status, and vice versa.

· When rejecting non-address information (such as the HELO command
argument or the client hostname/address), the Postfix SMTP
server will transform a sender or recipient DSN status into a
generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)
The default per-transport upper limit on the number of in-memory recip-
ients. These limits take priority over the global qmgr_message_recipi-
ent_limit after the message has been assigned to the respective trans-
ports. See also default_extra_recipient_limit and qmgr_message_recipi-
ent_minimum.

Use transport_recipient_limit to specify a transport-specific override,
where transport is the master.cf name of the message delivery trans-
port.

default_recipient_refill_delay (default: 5s)
The default per-transport maximum delay between recipients refills.
When not all message recipients fit into the memory at once, keep load-
ing more of them at least once every this many seconds. This is used
to make sure the recipients are refilled in timely manner even when
$default_recipient_refill_limit is too high for too slow deliveries.

Use transport_recipient_refill_delay to specify a transport-specific
override, where transport is the master.cf name of the message delivery
transport.

This feature is available in Postfix 2.4 and later.

default_recipient_refill_limit (default: 100)
The default per-transport limit on the number of recipients refilled at
once. When not all message recipients fit into the memory at once,
keep loading more of them in batches of at least this many at a time.
See also $default_recipient_refill_delay, which may result in recipient
batches lower than this when this limit is too high for too slow deliv-
eries.

Use transport_recipient_refill_limit to specify a transport-specific
override, where transport is the master.cf name of the message delivery
transport.

This feature is available in Postfix 2.4 and later.

default_transport (default: smtp)
The default mail delivery transport and next-hop destination for desti-
nations that do not match $mydestination, $inet_interfaces,
$proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains, or
$relay_domains. This information can be overruled with the
sender_dependent_default_transport_maps parameter and with the trans-
port(5) table.

In order of decreasing precedence, the nexthop destination is taken
from $sender_dependent_default_transport_maps, $default_transport,
$sender_dependent_relayhost_maps, $relayhost, or from the recipient
domain.

Specify a string of the form transport:nexthop, where transport is the
name of a mail delivery transport defined in master.cf. The :nexthop
destination is optional; its syntax is documented in the manual page of
the corresponding delivery agent.

Example:

default_transport = uucp:relayhostname

default_verp_delimiters (default: +=)
The two default VERP delimiter characters. These are used when no
explicit delimiters are specified with the SMTP XVERP command or with
the "sendmail -V" command-line option. Specify characters that are
allowed by the verp_delimiter_filter setting.

This feature is available in Postfix 1.1 and later.

defer_code (default: 450)
The numerical Postfix SMTP server response code when a remote SMTP
client request is rejected by the "defer" restriction.

Do not change this unless you have a complete understanding of RFC
2821.

defer_service_name (default: defer)
The name of the defer service. This service is implemented by the
bounce(8) daemon and maintains a record of failed delivery attempts and
generates non-delivery notifications.

This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)
The names of message delivery transports that should not deliver mail
unless someone issues "sendmail -q" or equivalent. Specify zero or more
names of mail delivery transports names that appear in the first field
of master.cf.

Example:

defer_transports = smtp

delay_logging_resolution_limit (default: 2)
The maximal number of digits after the decimal point when logging sub-
second delay values. Specify a number in the range 0..6.

Large delay values are rounded off to an integral number seconds; delay
values below the delay_logging_resolution_limit are logged as "0", and
small delay values are logged with at most two-digit precision.

The format of the "delays=a/b/c/d" logging is as follows:

· a = time from message arrival to last active queue entry

· b = time from last active queue entry to connection setup

· c = time in connection setup, including DNS, EHLO and STARTTLS

· d = time in message transmission

This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)
The recipient of postmaster notifications with the message headers of
mail that cannot be delivered within $delay_warning_time time units.

This feature is enabled with the delay_warning_time parameter.

delay_warning_time (default: 0h)
The time after which the sender receives the message headers of mail
that is still queued.

To enable this feature, specify a non-zero time value (an integral
value plus an optional one-letter suffix that specifies the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is h (hours).

deliver_lock_attempts (default: 20)
The maximal number of attempts to acquire an exclusive lock on a mail-
box file or bounce(8) logfile.

deliver_lock_delay (default: 1s)
The time between attempts to acquire an exclusive lock on a mailbox
file or bounce(8) logfile.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

destination_concurrency_feedback_debug (default: no)
Make the queue manager's feedback algorithm verbose for performance
analysis purposes.

This feature is available in Postfix 2.5 and later.

detect_8bit_encoding_header (default: yes)
Automatically detect 8BITMIME body content by looking at Content-Trans-
fer-Encoding: message headers; historically, this behavior was hard-
coded to be "always on".

This feature is available in Postfix 2.5 and later.

disable_dns_lookups (default: no)
Disable DNS lookups in the Postfix SMTP and LMTP clients. When dis-
abled, hosts are looked up with the getaddrinfo() system library rou-
tine which normally also looks in /etc/hosts.

DNS lookups are enabled by default.

disable_mime_input_processing (default: no)
Turn off MIME processing while receiving mail. This means that no spe-
cial treatment is given to Content-Type: message headers, and that all
text after the initial message headers is considered to be part of the
message body.

This feature is available in Postfix 2.0 and later.

Mime input processing is enabled by default, and is needed in order to
recognize MIME headers in message content.

disable_mime_output_conversion (default: no)
Disable the conversion of 8BITMIME format to 7BIT format. Mime output
conversion is needed when the destination does not advertise 8BITMIME
support.

This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)
Disable sending one bounce report per recipient.

The default, one per recipient, is what ezmlm needs.

This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)
Disable the SMTP VRFY command. This stops some techniques used to har-
vest email addresses.

Example:

disable_vrfy_command = no

dont_remove (default: 0)
Don't remove queue files and save them to the "saved" mail queue. This
is a debugging aid. To inspect the envelope information and content of
a Postfix queue file, use the postcat(1) command.

double_bounce_sender (default: double-bounce)
The sender address of postmaster notifications that are generated by
the mail system. All mail to this address is silently discarded, in
order to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)
The maximal number of addresses remembered by the address duplicate
filter for aliases(5) or virtual(5) alias expansion, or for showq(8)
queue displays.

empty_address_default_transport_maps_lookup_key (default: <>)
The sender_dependent_default_transport_maps search string that will be
used instead of the null sender address.

This feature is available in Postfix 2.7 and later.

empty_address_recipient (default: MAILER-DAEMON)
The recipient of mail addressed to the null address. Postfix does not
accept such addresses in SMTP commands, but they may still be created
locally as the result of configuration or software error.

empty_address_relayhost_maps_lookup_key (default: <>)
The sender_dependent_relayhost_maps search string that will be used
instead of the null sender address.

This feature is available in Postfix 2.5 and later. With earlier ver-
sions, sender_dependent_relayhost_maps lookups were skipped for the
null sender address.

enable_errors_to (default: no)
Report mail delivery errors to the address specified with the non-stan-
dard Errors-To: message header, instead of the envelope sender address
(this feature is removed with Postfix version 2.2, is turned off by
default with Postfix version 2.1, and is always turned on with older
Postfix versions).

enable_original_recipient (default: yes)
Enable support for the X-Original-To message header. This header is
needed for multi-recipient mailboxes.

When this parameter is set to yes, the cleanup(8) daemon performs
duplicate elimination on distinct pairs of (original recipient, rewrit-
ten recipient), and generates non-empty original recipient queue file
records.

When this parameter is set to no, the cleanup(8) daemon performs dupli-
cate elimination on the rewritten recipient address only, and generates
empty original recipient queue file records.

This feature is available in Postfix 2.1 and later. With Postfix ver-
sion 2.0, support for the X-Original-To message header is always turned
on. Postfix versions before 2.0 have no support for the X-Original-To
message header.

error_notice_recipient (default: postmaster)
The recipient of postmaster notifications about mail delivery problems
that are caused by policy, resource, software or protocol errors.
These notifications are enabled with the notify_classes parameter.

error_service_name (default: error)
The name of the error(8) pseudo delivery agent. This service always
returns mail as undeliverable.

This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)
Restrict the characters that the local(8) delivery agent allows in
$name expansions of $command_execution_directory. Characters outside
the allowed set are replaced by underscores.

This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)
When delivering to an alias "aliasname" that has an "owner-aliasname"
companion alias, set the envelope sender address to the expansion of
the "owner-aliasname" alias. Normally, Postfix sets the envelope sender
address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)
The list of environment variables that a Postfix process will export to
non-Postfix processes. The TZ variable is needed for sane time keeping
on System-V-ish systems.

Specify a list of names and/or name=value pairs, separated by white-
space or comma. The name=value form is supported with Postfix version
2.1 and later.

Example:

export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)
The maximal number of recipient addresses that Postfix will extract
from message headers when mail is submitted with "sendmail -t".

This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)
Optional list of relay hosts for SMTP destinations that can't be found
or that are unreachable. With Postfix 2.3 this parameter is renamed to
smtp_fallback_relay.

By default, mail is returned to the sender when a destination is not
found, and delivery is deferred when a destination is unreachable.

The fallback relays must be SMTP destinations. Specify a domain, host,
host:port, [host]:port, [address] or [address]:port; the form [host]
turns off MX lookups. If you specify multiple SMTP destinations, Post-
fix will try them in the specified order.

Note: before Postfix 2.2, do not use the fallback_relay feature when
relaying mail for a backup or primary MX domain. Mail would loop
between the Postfix MX host and the fallback_relay host when the final
destination is unavailable.

· In main.cf specify "relay_transport = relay",

· In master.cf specify "-o fallback_relay =" (i.e., empty) at the
end of the relay entry.

· In transport maps, specify "relay:nexthop..." as the right-hand
side for backup or primary MX domain entries.

Postfix version 2.2 and later will not use the fallback_relay feature
for destinations that it is MX host for.

fallback_transport (default: empty)
Optional message delivery transport that the local(8) delivery agent
should use for names that are not found in the aliases(5) or UNIX pass-
word database.

The precedence of local(8) delivery features from high to low is:
aliases, .forward files, mailbox_transport_maps, mailbox_transport,
mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_direc-
tory, fallback_transport_maps, fallback_transport and luser_relay.

fallback_transport_maps (default: empty)
Optional lookup tables with per-recipient message delivery transports
for recipients that the local(8) delivery agent could not find in the
aliases(5) or UNIX password database.

For safety reasons, this feature does not allow $number substitutions
in regular expression maps.

This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)
Optional list of destinations that are eligible for per-destination
logfiles with mail that is queued to those destinations.

By default, Postfix maintains "fast flush" logfiles only for destina-
tions that the Postfix SMTP server is willing to relay to (i.e. the
default is: "fast_flush_domains = $relay_domains"; see the
relay_domains parameter in the postconf(5) manual).

Specify a list of hosts or domains, "/file/name" patterns or "type:ta-
ble" lookup tables, separated by commas and/or whitespace. Continue
long lines by starting the next line with whitespace. A "/file/name"
pattern is replaced by its contents; a "type:table" lookup table is
matched when the domain or its parent domain appears as lookup key.

Specify "fast_flush_domains =" (i.e., empty) to disable the feature
altogether.

fast_flush_purge_time (default: 7d)
The time after which an empty per-destination "fast flush" logfile is
deleted.

You can specify the time as a number, or as a number followed by a let-
ter that indicates the time unit: s=seconds, m=minutes, h=hours,
d=days, w=weeks. The default time unit is days.

fast_flush_refresh_time (default: 12h)
The time after which a non-empty but unread per-destination "fast
flush" logfile needs to be refreshed. The contents of a logfile are
refreshed by requesting delivery of all messages listed in the logfile.

You can specify the time as a number, or as a number followed by a let-
ter that indicates the time unit: s=seconds, m=minutes, h=hours,
d=days, w=weeks. The default time unit is hours.

fault_injection_code (default: 0)
Force specific internal tests to fail, to test the handling of errors
that are difficult to reproduce otherwise.

flush_service_name (default: flush)
The name of the flush(8) service. This service maintains per-destina-
tion logfiles with the queue file names of mail that is queued for
those destinations.

This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)
The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)
The delay between attempts to fork() a child process.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

forward_expansion_filter (default: see postconf -d output)
Restrict the characters that the local(8) delivery agent allows in
$name expansions of $forward_path. Characters outside the allowed set
are replaced by underscores.

forward_path (default: see postconf -d output)
The local(8) delivery agent search list for finding a .forward file
with user-specified delivery methods. The first file that is found is
used.

The following $name expansions are done on forward_path before the
search actually happens. The result of $name expansion is filtered with
the character set that is specified with the forward_expansion_filter
parameter.

$user The recipient's username.

$shell The recipient's login shell pathname.

$home The recipient's home directory.

$recipient
The full recipient address.

$extension
The optional recipient address extension.

$domain
The recipient domain.

$local The entire recipient localpart.

$recipient_delimiter
The system-wide recipient address extension delimiter.

${name?value}
Expands to value when $name is non-empty.

${name:value}
Expands to value when $name is empty.

Instead of $name you can also specify ${name} or $(name).

Examples:

forward_path = /var/forward/$user
forward_path =
/var/forward/$user/.forward$recipient_delimiter$extension,
/var/forward/$user/.forward

frozen_delivered_to (default: yes)
Update the local(8) delivery agent's idea of the Delivered-To: address
(see prepend_delivered_header) only once, at the start of a delivery
attempt; do not update the Delivered-To: address while expanding
aliases or .forward files.

This feature is available in Postfix 2.3 and later. With older Postfix
releases, the behavior is as if this parameter is set to "no". The old
setting can be expensive with deeply nested aliases or .forward files.
When an alias or .forward file changes the Delivered-To: address, it
ties up one queue file and one cleanup process instance while mail is
being forwarded.

hash_queue_depth (default: 1)
The number of subdirectory levels for queue directories listed with the
hash_queue_names parameter.

After changing the hash_queue_names or hash_queue_depth parameter, exe-
cute the command "postfix reload".

hash_queue_names (default: deferred, defer)
The names of queue directories that are split across multiple subdirec-
tory levels.

Before Postfix version 2.2, the default list of hashed queues was sig-
nificantly larger. Claims about improvements in file system technology
suggest that hashing of the incoming and active queues is no longer
needed. Fewer hashed directories speed up the time needed to restart
Postfix.

After changing the hash_queue_names or hash_queue_depth parameter, exe-
cute the command "postfix reload".

header_address_token_limit (default: 10240)
The maximal number of address tokens are allowed in an address message
header. Information that exceeds the limit is discarded. The limit is
enforced by the cleanup(8) server.

header_checks (default: empty)
Optional lookup tables for content inspection of primary non-MIME mes-
sage headers, as specified in the header_checks(5) manual page.

header_size_limit (default: 102400)
The maximal amount of memory in bytes for storing a message header. If
a header is larger, the excess is discarded. The limit is enforced by
the cleanup(8) server.

helpful_warnings (default: yes)
Log warnings about problematic configuration settings, and provide
helpful suggestions.

This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)
Optional pathname of a mailbox file relative to a local(8) user's home
directory.

Specify a pathname ending in "/" for qmail-style delivery.

Examples:

home_mailbox = Mailbox
home_mailbox = Maildir/

hopcount_limit (default: 50)
The maximal number of Received: message headers that is allowed in the
primary message headers. A message that exceeds the limit is bounced,
in order to stop a mailer loop.

html_directory (default: see postconf -d output)
The location of Postfix HTML files that describe how to build, config-
ure or operate a specific Postfix subsystem or feature.

ignore_mx_lookup_error (default: no)
Ignore DNS MX lookups that produce no response. By default, the Post-
fix SMTP client defers delivery and tries again after some delay. This
behavior is required by the SMTP standard.

Specify "ignore_mx_lookup_error = yes" to force a DNS A record lookup
instead. This violates the SMTP standard and can result in mis-delivery
of mail.

import_environment (default: see postconf -d output)
The list of environment parameters that a Postfix process will import
from a non-Postfix parent process. Examples of relevant parameters:

TZ Needed for sane time keeping on most System-V-ish systems.

DISPLAY
Needed for debugging Postfix daemons with an X-windows debugger.

XAUTHORITY
Needed for debugging Postfix daemons with an X-windows debugger.

MAIL_CONFIG
Needed to make "postfix -c" work.

Specify a list of names and/or name=value pairs, separated by white-
space or comma. The name=value form is supported with Postfix version
2.1 and later.

in_flow_delay (default: 1s)
Time to pause before accepting a new message, when the message arrival
rate exceeds the message delivery rate. This feature is turned on by
default (it's disabled on SCO UNIX due to an SCO bug).

With the default 100 SMTP server process limit, "in_flow_delay = 1s"
limits the mail inflow to 100 messages per second above the number of
messages delivered per second.

Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)
The network interface addresses that this mail system receives mail on.
Specify "all" to receive mail on all network interfaces (default), and
"loopback-only" to receive mail on loopback network interfaces only
(Postfix version 2.2 and later). The parameter also controls delivery
of mail to user@[ip.address].

Note 1: you need to stop and start Postfix when this parameter changes.

Note 2: address information may be enclosed inside [], but this form is
not required here.

When inet_interfaces specifies just one IPv4 and/or IPv6 address that
is not a loopback address, the Postfix SMTP client will use this
address as the IP source address for outbound mail. Support for IPv6 is
available in Postfix version 2.2 and later.

On a multi-homed firewall with separate Postfix instances listening on
the "inside" and "outside" interfaces, this can prevent each instance
from being able to reach servers on the "other side" of the firewall.
Setting smtp_bind_address to 0.0.0.0 avoids the potential problem for
IPv4, and setting smtp_bind_address6 to :: solves the problem for IPv6.

A better solution for multi-homed firewalls is to leave inet_interfaces
at the default value and instead use explicit IP addresses in the mas-
ter.cf SMTP server definitions. This preserves the Postfix SMTP
client's loop detection, by ensuring that each side of the firewall
knows that the other IP address is still the same host. Setting
$inet_interfaces to a single IPv4 and/or IPV6 address is primarily use-
ful with virtual hosting of domains on secondary IP addresses, when
each IP address serves a different domain (and has a different $myhost-
name setting).

See also the proxy_interfaces parameter, for network addresses that are
forwarded to Postfix by way of a proxy or address translator.

Examples:

inet_interfaces = all (DEFAULT)
inet_interfaces = loopback-only (Postfix version 2.2 and later)
inet_interfaces = 127.0.0.1
inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: ipv4)
The Internet protocols Postfix will attempt to use when making or
accepting connections. Specify one or more of "ipv4" or "ipv6", sepa-
rated by whitespace or commas. The form "all" is equivalent to "ipv4,
ipv6" or "ipv4", depending on whether the operating system implements
IPv6.

This feature is available in Postfix 2.2 and later.

Note: you MUST stop and start Postfix after changing this parameter.

On systems that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server
will also accept IPv4 connections, even when IPv4 is turned off with
the inet_protocols parameter. On systems with IPV6_V6ONLY support,
Postfix will use separate server sockets for IPv6 and IPv4, and each
will accept only connections for the corresponding protocol.

When IPv4 support is enabled via the inet_protocols parameter, Postfix
will to DNS type A record lookups, and will convert IPv4-in-IPv6 client
IP addresses (::ffff:1.2.3.4) to their original IPv4 form (1.2.3.4).
The latter is needed on hosts that pre-date IPV6_V6ONLY support (RFC
3493).

When IPv6 support is enabled via the inet_protocols parameter, Postfix
will do DNS type AAAA record lookups.

When both IPv4 and IPv6 support are enabled, the Postfix SMTP client
will attempt to connect via IPv6 before attempting to use IPv4.

Examples:

inet_protocols = ipv4 (DEFAULT)
inet_protocols = all
inet_protocols = ipv6
inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)
The initial per-destination concurrency level for parallel delivery to
the same destination. With per-destination recipient limit > 1, a des-
tination is a domain, otherwise it is a recipient.

Use transport_initial_destination_concurrency to specify a transport-
specific override, where transport is the master.cf name of the message
delivery transport (Postfix 2.5 and later).

Warning: with concurrency of 1, one bad message can be enough to block
all mail to a site.

internal_mail_filter_classes (default: empty)
What categories of Postfix-generated mail are subject to before-queue
content inspection by non_smtpd_milters, header_checks and body_checks.
Specify zero or more of the following, separated by whitespace or
comma.

bounce Inspect the content of delivery status notifications.

notify Inspect the content of postmaster notifications by the smtp(8)
and smtpd(8) processes.

NOTE: It's generally not safe to enable content inspection of Postfix-
generated email messages. The user is warned.

This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)
The numerical Postfix SMTP server response code when the client HELO or
EHLO command parameter is rejected by the reject_invalid_helo_hostname
restriction.

Do not change this unless you have a complete understanding of RFC
2821.

ipc_idle (default: version dependent)
The time after which a client closes an idle internal communication
channel. The purpose is to allow servers to terminate voluntarily
after they become idle. This is used, for example, by the address
resolving and rewriting clients.

With Postfix 2.4 the default value was reduced from 100s to 5s.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

ipc_timeout (default: 3600s)
The time limit for sending or receiving information over an internal
communication channel. The purpose is to break out of deadlock situa-
tions. If the time limit is exceeded the software aborts with a fatal
error.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

ipc_ttl (default: 1000s)
The time after which a client closes an active internal communication
channel. The purpose is to allow servers to terminate voluntarily
after reaching their client limit. This is used, for example, by the
address resolving and rewriting clients.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)
Upon input, long lines are chopped up into pieces of at most this
length; upon delivery, long lines are reconstructed.

lmtp_assume_final (default: no)
When an LMTP server announces no DSN support, assume that the server
performs final delivery, and send "delivered" delivery status notifica-
tions instead of "relayed". The default setting is backwards compatible
to avoid the infinetisimal possibility of breaking existing LMTP-based
content filters.

lmtp_bind_address (default: empty)
The LMTP-specific version of the smtp_bind_address configuration param-
eter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)
The LMTP-specific version of the smtp_bind_address6 configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_body_checks (default: empty)
The LMTP-specific version of the smtp_body_checks configuration parame-
ter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_cache_connection (default: yes)
Keep Postfix LMTP client connections open for up to $max_idle seconds.
When the LMTP client receives a request for the same connection the
connection is reused.

This parameter is available in Postfix version 2.2 and earlier. With
Postfix version 2.3 and later, see lmtp_connection_cache_on_demand,
lmtp_connection_cache_destinations, or lmtp_connection_re-
use_time_limit.

The effectiveness of cached connections will be determined by the num-
ber of LMTP servers in use, and the concurrency limit specified for the
LMTP client. Cached connections are closed under any of the following
conditions:

· The LMTP client idle time limit is reached. This limit is spec-
ified with the Postfix max_idle configuration parameter.

· A delivery request specifies a different destination than the
one currently cached.

· The per-process limit on the number of delivery requests is
reached. This limit is specified with the Postfix max_use con-
figuration parameter.

· Upon the onset of another delivery request, the LMTP server
associated with the current session does not respond to the RSET
command.

Most of these limitations will be removed after Postfix implements a
connection cache that is shared among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)
The LMTP-specific version of the smtp_cname_overrides_servername con-
figuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)
The LMTP client time limit for completing a TCP connection, or zero
(use the operating system built-in time limit). When no connection can
be made within the deadline, the LMTP client tries the next address on
the mail exchanger list.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

Example:

lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)
The LMTP-specific version of the smtp_connection_cache_destinations
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)
The LMTP-specific version of the smtp_connection_cache_on_demand con-
figuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)
The LMTP-specific version of the smtp_connection_cache_time_limit con-
figuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_time_limit (default: 300s)
The LMTP-specific version of the smtp_connection_reuse_time_limit con-
figuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)
The LMTP client time limit for sending the LMTP ".", and for receiving
the server response. When no response is received within the deadline,
a warning is logged that the mail may be delivered multiple times.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_data_init_timeout (default: 120s)
The LMTP client time limit for sending the LMTP DATA command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_data_xfer_timeout (default: 180s)
The LMTP client time limit for sending the LMTP message content. When
the connection stalls for more than $lmtp_data_xfer_timeout the LMTP
client terminates the transfer.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_defer_if_no_mx_address_found (default: no)
The LMTP-specific version of the smtp_defer_if_no_mx_address_found con-
figuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_destination_concurrency_limit (default: $default_destination_concur-
rency_limit)
The maximal number of parallel deliveries to the same destination via
the lmtp message delivery transport. This limit is enforced by the
queue manager. The message delivery transport name is the first field
in the entry in the master.cf file.

lmtp_destination_recipient_limit (default: $default_destination_recipi-
ent_limit)
The maximal number of recipients per message for the lmtp message
delivery transport. This limit is enforced by the queue manager. The
message delivery transport name is the first field in the entry in the
master.cf file.

Setting this parameter to a value of 1 changes the meaning of lmtp_des-
tination_concurrency_limit from concurrency per domain into concurrency
per recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)
Lookup tables, indexed by the remote LMTP server address, with case
insensitive lists of LHLO keywords (pipelining, starttls, auth, etc.)
that the LMTP client will ignore in the LHLO response from a remote
LMTP server. See lmtp_discard_lhlo_keywords for details. The table is
not indexed by hostname for consistency with smtpd_discard_ehlo_key-
word_address_maps.

This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)
A case insensitive list of LHLO keywords (pipelining, starttls, auth,
etc.) that the LMTP client will ignore in the LHLO response from a
remote LMTP server.

This feature is available in Postfix 2.3 and later.

Notes:

· Specify the silent-discard pseudo keyword to prevent this action
from being logged.

· Use the lmtp_discard_lhlo_keyword_address_maps feature to dis-
card LHLO keywords selectively.

lmtp_enforce_tls (default: no)
The LMTP-specific version of the smtp_enforce_tls configuration parame-
ter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_generic_maps (default: empty)
The LMTP-specific version of the smtp_generic_maps configuration param-
eter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_header_checks (default: empty)
The LMTP-specific version of the smtp_header_checks configuration
parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_host_lookup (default: dns)
The LMTP-specific version of the smtp_host_lookup configuration parame-
ter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)
The hostname to send in the LMTP LHLO command.

The default value is the machine hostname. Specify a hostname or
[ip.add.re.ss].

This information can be specified in the main.cf file for all LMTP
clients, or it can be specified in the master.cf file for a specific
client, for example:

/etc/postfix/master.cf:
mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)
The LMTP client time limit for sending the LHLO command, and for
receiving the initial server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_line_length_limit (default: 990)
The LMTP-specific version of the smtp_line_length_limit configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)
The LMTP client time limit for sending the MAIL FROM command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_mime_header_checks (default: empty)
The LMTP-specific version of the smtp_mime_header_checks configuration
parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_mx_address_limit (default: 5)
The LMTP-specific version of the smtp_mx_address_limit configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)
The LMTP-specific version of the smtp_mx_session_limit configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_nested_header_checks (default: empty)
The LMTP-specific version of the smtp_nested_header_checks configura-
tion parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_pix_workaround_delay_time (default: 10s)
The LMTP-specific version of the smtp_pix_workaround_delay_time config-
uration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)
The LMTP-specific version of the smtp_pix_workaround_maps configuration
parameter. See there for details.

This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)
The LMTP-specific version of the smtp_pix_workaround_threshold_time
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)
The LMTP-specific version of the smtp_pix_workaround configuration
parameter. See there for details.

This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)
The LMTP client time limit for sending the QUIT command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_quote_rfc821_envelope (default: yes)
The LMTP-specific version of the smtp_quote_rfc821_envelope configura-
tion parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)
The LMTP-specific version of the smtp_randomize_addresses configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)
The LMTP client time limit for sending the RCPT TO command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_reply_filter (default: empty)
The LMTP-specific version of the smtp_reply_filter configuration param-
eter. See there for details.

This feature is available in Postfix 2.7 and later.

lmtp_rset_timeout (default: 20s)
The LMTP client time limit for sending the RSET command, and for
receiving the server response. The LMTP client sends RSET in order to
finish a recipient address probe, or to verify that a cached connection
is still alive.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

lmtp_sasl_auth_cache_name (default: empty)
The LMTP-specific version of the smtp_sasl_auth_cache_name configura-
tion parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_cache_time (default: 90d)
The LMTP-specific version of the smtp_sasl_auth_cache_time configura-
tion parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_enable (default: no)
Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_auth_soft_bounce (default: yes)
The LMTP-specific version of the smtp_sasl_auth_soft_bounce configura-
tion parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_sasl_mechanism_filter (default: empty)
The LMTP-specific version of the smtp_sasl_mechanism_filter configura-
tion parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)
Optional LMTP client lookup tables with one username:password entry per
host or domain. If a remote host or domain has no username:password
entry, then the Postfix LMTP client will not attempt to authenticate to
the remote host.

lmtp_sasl_path (default: empty)
Implementation-specific information that is passed through to the SASL
plug-in implementation that is selected with lmtp_sasl_type. Typically
this specifies the name of a configuration file or rendezvous point.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)
SASL security options; as of Postfix 2.3 the list of available features
depends on the SASL client implementation that is selected with
lmtp_sasl_type.

The following security features are defined for the cyrus client SASL
implementation:

noplaintext
Disallow authentication methods that use plaintext passwords.

noactive
Disallow authentication methods that are vulnerable to non-dic-
tionary active attacks.

nodictionary
Disallow authentication methods that are vulnerable to passive
dictionary attack.

noanonymous
Disallow anonymous logins.

Example:

lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
The LMTP-specific version of the smtp_sasl_tls_security_options config-
uration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options (default: $lmtp_sasl_tls_secu-
rity_options)
The LMTP-specific version of the smtp_sasl_tls_verified_secu-
rity_options configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)
The SASL plug-in type that the Postfix LMTP client should use for
authentication. The available types are listed with the "postconf -A"
command.

This feature is available in Postfix 2.3 and later.

lmtp_send_xforward_command (default: no)
Send an XFORWARD command to the LMTP server when the LMTP LHLO server
response announces XFORWARD support. This allows an lmtp(8) delivery
agent, used for content filter message injection, to forward the name,
address, protocol and HELO name of the original client to the content
filter and downstream queuing LMTP server. Before you change the value
to yes, it is best to make sure that your content filter supports this
command.

This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)
The LMTP-specific version of the smtp_sender_dependent_authentication
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)
The LMTP-specific version of the smtp_skip_5xx_greeting configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)
Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)
The LMTP-specific version of the smtp_starttls_timeout configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)
The default TCP port that the Postfix LMTP client connects to.

lmtp_tls_CAfile (default: empty)
The LMTP-specific version of the smtp_tls_CAfile configuration parame-
ter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)
The LMTP-specific version of the smtp_tls_CApath configuration parame-
ter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_block_early_mail_reply (default: empty)
The LMTP-specific version of the smtp_tls_block_early_mail_reply con-
figuration parameter. See there for details.

This feature is available in Postfix 2.7 and later.

lmtp_tls_cert_file (default: empty)
The LMTP-specific version of the smtp_tls_cert_file configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_ciphers (default: export)
The LMTP-specific version of the smtp_tls_ciphers configuration parame-
ter. See there for details.

This feature is available in Postfix 2.6 and later.

lmtp_tls_dcert_file (default: empty)
The LMTP-specific version of the smtp_tls_dcert_file configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
The LMTP-specific version of the smtp_tls_dkey_file configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_eccert_file (default: empty)
The LMTP-specific version of the smtp_tls_eccert_file configuration
parameter. See there for details.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_eckey_file (default: empty)
The LMTP-specific version of the smtp_tls_eckey_file configuration
parameter. See there for details.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_enforce_peername (default: yes)
The LMTP-specific version of the smtp_tls_enforce_peername configura-
tion parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)
The LMTP-specific version of the smtp_tls_exclude_ciphers configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_fingerprint_cert_match (default: empty)
The LMTP-specific version of the smtp_tls_fingerprint_cert_match con-
figuration parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_tls_fingerprint_digest (default: md5)
The LMTP-specific version of the smtp_tls_fingerprint_digest configura-
tion parameter. See there for details.

This feature is available in Postfix 2.5 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)
The LMTP-specific version of the smtp_tls_key_file configuration param-
eter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)
The LMTP-specific version of the smtp_tls_loglevel configuration param-
eter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: empty)
The LMTP-specific version of the smtp_tls_mandatory_ciphers configura-
tion parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)
The LMTP-specific version of the smtp_tls_mandatory_exclude_ciphers
configuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: SSLv3, TLSv1)
The LMTP-specific version of the smtp_tls_mandatory_protocols configu-
ration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)
The LMTP-specific version of the smtp_tls_note_starttls_offer configu-
ration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)
The LMTP-specific version of the smtp_tls_per_site configuration param-
eter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)
The LMTP-specific version of the smtp_tls_policy_maps configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_protocols (default: empty)
The LMTP-specific version of the smtp_tls_protocols configuration
parameter. See there for details.

This feature is available in Postfix 2.6 and later.

lmtp_tls_scert_verifydepth (default: 9)
The LMTP-specific version of the smtp_tls_scert_verifydepth configura-
tion parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)
The LMTP-specific version of the smtp_tls_secure_cert_match configura-
tion parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_security_level (default: empty)
The LMTP-specific version of the smtp_tls_security_level configuration
parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_database (default: empty)
The LMTP-specific version of the smtp_tls_session_cache_database con-
figuration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)
The LMTP-specific version of the smtp_tls_session_cache_timeout config-
uration parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_tls_verify_cert_match (default: hostname)
The LMTP-specific version of the smtp_tls_verify_cert_match configura-
tion parameter. See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)
The LMTP-specific version of the smtp_use_tls configuration parameter.
See there for details.

This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)
The LMTP client time limit for sending the XFORWARD command, and for
receiving the server response.

In case of problems the client does NOT try the next address on the
mail exchanger list.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)
Optional shell program for local(8) delivery to non-Postfix command.
By default, non-Postfix commands are executed directly; commands are
given to given to /bin/sh only when they contain shell meta characters
or shell built-in commands.

"sendmail's restricted shell" (smrsh) is what most people will use in
order to restrict what programs can be run from e.g. .forward files
(smrsh is part of the Sendmail distribution).

Note: when a shell program is specified, it is invoked even when the
command contains no shell built-in commands or meta characters.

Example:

local_command_shell = /some/where/smrsh -c

local_destination_concurrency_limit (default: 2)
The maximal number of parallel deliveries via the local mail delivery
transport to the same recipient (when "local_destination_recipi-
ent_limit = 1") or the maximal number of parallel deliveries to the
same local domain (when "local_destination_recipient_limit > 1"). This
limit is enforced by the queue manager. The message delivery transport
name is the first field in the entry in the master.cf file.

A low limit of 2 is recommended, just in case someone has an expensive
shell command in a .forward file or in an alias (e.g., a mailing list
manager). You don't want to run lots of those at the same time.

local_destination_recipient_limit (default: 1)
The maximal number of recipients per message delivery via the local
mail delivery transport. This limit is enforced by the queue manager.
The message delivery transport name is the first field in the entry in
the master.cf file.

Setting this parameter to a value > 1 changes the meaning of local_des-
tination_concurrency_limit from concurrency per recipient into concur-
rency per domain.

local_header_rewrite_clients (default: permit_inet_interfaces)
Rewrite message header addresses in mail from these clients and update
incomplete addresses with the domain name in $myorigin or $mydomain;
either don't rewrite message headers from other clients at all, or re-
write message headers and update incomplete addresses with the domain
specified in the remote_header_rewrite_domain parameter.

See the append_at_myorigin and append_dot_mydomain parameters for
details of how domain names are appended to incomplete addresses.

Specify a list of zero or more of the following:

permit_inet_interfaces
Append the domain name in $myorigin or $mydomain when the client
IP address matches $inet_interfaces. This is enabled by default.

permit_mynetworks
Append the domain name in $myorigin or $mydomain when the client
IP address matches any network or network address listed in
$mynetworks. This setting will not prevent remote mail header
address rewriting when mail from a remote client is forwarded by
a neighboring system.

permit_sasl_authenticated
Append the domain name in $myorigin or $mydomain when the client
is successfully authenticated via the RFC 4954 (AUTH) protocol.

permit_tls_clientcerts
Append the domain name in $myorigin or $mydomain when the client
TLS certificate fingerprint is listed in $relay_clientcerts.
The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior
to Postfix version 2.5).

permit_tls_all_clientcerts
Append the domain name in $myorigin or $mydomain when the client
TLS certificate is successfully verified, regardless of whether
it is listed on the server, and regardless of the certifying
authority.

check_address_map type:table

type:table
Append the domain name in $myorigin or $mydomain when the client
IP address matches the specified lookup table. The lookup
result is ignored, and no subnet lookup is done. This is suit-
able for, e.g., pop-before-smtp lookup tables.

Examples:

The Postfix < 2.2 backwards compatible setting: always rewrite message
headers, and always append my own domain to incomplete header
addresses.

local_header_rewrite_clients = static:all

The purist (and default) setting: rewrite headers only in mail from
Postfix sendmail and in SMTP mail from this machine.

local_header_rewrite_clients = permit_inet_interfaces

The intermediate setting: rewrite header addresses and append $myorigin
or $mydomain information only with mail from Postfix sendmail, from
local clients, or from authorized SMTP clients.

Note: this setting will not prevent remote mail header address rewrit-
ing when mail from a remote client is forwarded by a neighboring sys-
tem.

local_header_rewrite_clients = permit_mynetworks,
permit_sasl_authenticated permit_tls_clientcerts
check_address_map hash:/etc/postfix/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
Lookup tables with all names or addresses of local recipients: a recip-
ient address is local when its domain matches $mydestination,
$inet_interfaces or $proxy_interfaces. Specify @domain as a wild-card
for domains that do not have a valid recipient list. Technically,
tables listed with $local_recipient_maps are used as lists: Postfix
needs to know only if a lookup string is found or not, but it does not
use the result from table lookup.

If this parameter is non-empty (the default), then the Postfix SMTP
server will reject mail for unknown local users.

To turn off local recipient checking in the Postfix SMTP server, spec-
ify "local_recipient_maps =" (i.e. empty).

The default setting assumes that you use the default Postfix local
delivery agent for local delivery. You need to update the local_recipi-
ent_maps setting if:

· You redefine the local delivery agent in master.cf.

· You redefine the "local_transport" setting in main.cf.

· You use the "luser_relay", "mailbox_transport", or "fall-
back_transport" feature of the Postfix local(8) delivery agent.

Details are described in the LOCAL_RECIPIENT_README file.

Beware: if the Postfix SMTP server runs chrooted, you need to access
the passwd file via the proxymap(8) service, in order to overcome
chroot access restrictions. The alternative, maintaining a copy of the
system password file in the chroot jail is not practical.

Examples:

local_recipient_maps =

local_transport (default: local:$myhostname)
The default mail delivery transport and next-hop destination for final
delivery to domains listed with mydestination, and for [ipaddress] des-
tinations that match $inet_interfaces or $proxy_interfaces. This
information can be overruled with the transport(5) table.

By default, local mail is delivered to the transport called "local",
which is just the name of a service that is defined the master.cf file.

Beware: if you override the default local delivery agent then you need
to review the LOCAL_RECIPIENT_README document, otherwise the SMTP
server may reject mail for local recipients.

luser_relay (default: empty)
Optional catch-all destination for unknown local(8) recipients. By
default, mail for unknown recipients in domains that match $mydestina-
tion, $inet_interfaces or $proxy_interfaces is returned as undeliver-
able.

The following $name expansions are done on luser_relay:

$domain
The recipient domain.

$extension
The recipient address extension.

$home The recipient's home directory.

$local The entire recipient address localpart.

$recipient
The full recipient address.

$recipient_delimiter
The system-wide recipient address extension delimiter.

$shell The recipient's login shell.

$user The recipient username.

${name?value}
Expands to value when $name has a non-empty value.

${name:value}
Expands to value when $name has an empty value.

Instead of $name you can also specify ${name} or $(name).

Note: luser_relay works only for the Postfix local(8) delivery agent.

Note: if you use this feature for accounts not in the UNIX password
file, then you must specify "local_recipient_maps =" (i.e. empty) in
the main.cf file, otherwise the Postfix SMTP server will reject mail
for non-UNIX accounts with "User unknown in local recipient table".

Examples:

luser_relay = $user@other.host
luser_relay = $local@other.host
luser_relay = admin+$local

mail_name (default: Postfix)
The mail system name that is displayed in Received: headers, in the
SMTP greeting banner, and in bounced mail.

mail_owner (default: postfix)
The UNIX system account that owns the Postfix queue and most Postfix
daemon processes. Specify the name of a user account that does not
share a group with other accounts and that owns no other files or pro-
cesses on the system. In particular, don't specify nobody or daemon.
PLEASE USE A DEDICATED USER ID AND GROUP ID.

When this parameter value is changed you need to re-run "postfix set-
permissions" (with Postfix version 2.0 and earlier: "/etc/postfix/post-
install set-permissions".

mail_release_date (default: see postconf -d output)
The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)
The directory where local(8) UNIX-style mailboxes are kept. The default
setting depends on the system type. Specify a name ending in / for
maildir-style delivery.

Note: maildir delivery is done with the privileges of the recipient.
If you use the mail_spool_directory setting for maildir style delivery,
then you must create the top-level maildir directory in advance. Post-
fix will not create it.

Examples:

mail_spool_directory = /var/mail
mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)
The version of the mail system. Stable releases are named
major.minor.patchlevel. Experimental releases also include the release
date. The version string can be used in, for example, the SMTP greeting
banner.

mailbox_command (default: empty)
Optional external command that the local(8) delivery agent should use
for mailbox delivery. The command is run with the user ID and the pri-
mary group ID privileges of the recipient. Exception: command delivery
for root executes with $default_privs privileges. This is not a prob-
lem, because 1) mail for root should always be aliased to a real user
and 2) don't log in as root, use "su" instead.

The following environment variables are exported to the command:

CLIENT_ADDRESS
Remote client network address. Available in Postfix version 2.2
and later.

CLIENT_HELO
Remote client EHLO command parameter. Available in Postfix ver-
sion 2.2 and later.

CLIENT_HOSTNAME
Remote client hostname. Available in Postfix version 2.2 and
later.

CLIENT_PROTOCOL
Remote client protocol. Available in Postfix version 2.2 and
later.

DOMAIN The domain part of the recipient address.

EXTENSION
The optional address extension.

HOME The recipient home directory.

LOCAL The recipient address localpart.

LOGNAME
The recipient's username.

ORIGINAL_RECIPIENT
The entire recipient address, before any address rewriting or
aliasing.

RECIPIENT
The full recipient address.

SASL_METHOD
SASL authentication method specified in the remote client AUTH
command. Available in Postfix version 2.2 and later.

SASL_SENDER
SASL sender address specified in the remote client MAIL FROM
command. Available in Postfix version 2.2 and later.

SASL_USER
SASL username specified in the remote client AUTH command.
Available in Postfix version 2.2 and later.

SENDER The full sender address.

SHELL The recipient's login shell.

USER The recipient username.

Unlike other Postfix configuration parameters, the mailbox_command
parameter is not subjected to $name substitutions. This is to make it
easier to specify shell syntax (see example below).

If you can, avoid shell meta characters because they will force Postfix
to run an expensive shell process. If you're delivering via Procmail
then running a shell won't make a noticeable difference in the total
cost.

Note: if you use the mailbox_command feature to deliver mail system-
wide, you must set up an alias that forwards mail for root to a real
user.

Examples:

mailbox_command = /some/where/procmail
mailbox_command = /some/where/procmail -a "$EXTENSION"
mailbox_command = /some/where/maildrop -d "$USER"
-f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)
Optional lookup tables with per-recipient external commands to use for
local(8) mailbox delivery. Behavior is as with mailbox_command.

mailbox_delivery_lock (default: see postconf -d output)
How to lock a UNIX-style local(8) mailbox before attempting delivery.
For a list of available file locking methods, use the "postconf -l"
command.

This setting is ignored with maildir style delivery, because such
deliveries are safe without explicit locks.

Note: The dotlock method requires that the recipient UID or GID has
write access to the parent directory of the mailbox file.

Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)
The maximal size of any local(8) individual mailbox or maildir file, or
zero (no limit). In fact, this limits the size of any file that is
written to upon local delivery, including files written by external
commands that are executed by the local(8) delivery agent.

This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)
Optional message delivery transport that the local(8) delivery agent
should use for mailbox delivery to all local recipients, whether or not
they are found in the UNIX passwd database.

mailbox_transport_maps (default: empty)
Optional lookup tables with per-recipient message delivery transports
to use for local(8) mailbox delivery, whether or not the recipients are
found in the UNIX passwd database.

For safety reasons, this feature does not allow $number substitutions
in regular expression maps.

This feature is available in Postfix 2.3 and later.

mailq_path (default: see postconf -d output)
Sendmail compatibility feature that specifies where the Postfix
mailq(1) command is installed. This command can be used to list the
Postfix mail queue.

manpage_directory (default: see postconf -d output)
Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)
Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)
The numerical Postfix SMTP server response code when a remote SMTP
client request is blocked by the reject_rbl_client,
reject_rhsbl_client, reject_rhsbl_sender or reject_rhsbl_recipient
restriction.

Do not change this unless you have a complete understanding of RFC
2821.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)

What addresses are subject to address masquerading.

By default, address masquerading is limited to envelope sender
addresses, and to header sender and header recipient addresses. This
allows you to use address masquerading on a mail gateway while still
being able to forward mail to users on individual machines.

Specify zero or more of: envelope_sender, envelope_recipient,
header_sender, header_recipient

masquerade_domains (default: empty)
Optional list of domains whose subdomain structure will be stripped off
in email addresses.

The list is processed left to right, and processing stops at the first
match. Thus,

masquerade_domains = foo.example.com example.com

strips "user@any.thing.foo.example.com" to "user@foo.example.com", but
strips "user@any.thing.else.example.com" to "user@example.com".

A domain name prefixed with ! means do not masquerade this domain or
its subdomains. Thus,

masquerade_domains = !foo.example.com example.com

does not change "user@any.thing.foo.example.com" or "user@foo.exam-
ple.com", but strips "user@any.thing.else.example.com" to "user@exam-
ple.com".

Note: with Postfix version 2.2, message header address masquerading
happens only when message header address rewriting is enabled:

· The message is received with the Postfix sendmail(1) command,

· The message is received from a network client that matches
$local_header_rewrite_clients,

· The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty
value.

To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all".

Example:

masquerade_domains = $mydomain

masquerade_exceptions (default: empty)
Optional list of user names that are not subjected to address mas-
querading, even when their address matches $masquerade_domains.

By default, address masquerading makes no exceptions.

Examples:

masquerade_exceptions = root, mailer-daemon
masquerade_exceptions = root

master_service_disable (default: empty)
Selectively disable master(8) listener ports by service type or by ser-
vice name and type. Specify a list of service types ("inet", "unix",
"fifo", or "pass") or "name.type" tuples, where "name" is the first
field of a master.cf entry and "type" is a service type. As with other
Postfix matchlists, a search stops at the first match. Specify "!pat-
tern" to exclude a service from the list. By default, all master(8)
listener ports are enabled.

Note: this feature does not support "/file/name" or "type:table" pat-
terns, nor does it support wildcards such as "*" or "all". This is
intentional.

Examples:

# Turn on all master(8) listener ports (the default).
master_service_disable =
# Turn off only the main SMTP listener port.
master_service_disable = smtp.inet
# Turn off all TCP/IP listener ports.
master_service_disable = inet
# Turn off all TCP/IP listener ports except "foo".
master_service_disable = !foo.inet, inet

This feature is available in Postfix 2.6 and later.

max_idle (default: 100s)
The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily. This param-
eter is ignored by the Postfix queue manager and by other long-lived
Postfix daemon processes.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

max_use (default: 100)
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily. This parameter is
ignored by the Postfix queue manager and by other long-lived Postfix
daemon processes.

maximal_backoff_time (default: 4000s)
The maximal time between attempts to deliver a deferred message.

This parameter should be set to a value greater than or equal to $mini-
mal_backoff_time. See also $queue_run_delay.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

maximal_queue_lifetime (default: 5d)
The maximal time a message is queued before it is sent back as undeliv-
erable.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is d (days).

Specify 0 when mail delivery should be tried only once.

message_reject_characters (default: empty)
The set of characters that Postfix will reject in message content. The
usual C-like escape sequences are recognized: \a \b \f \n \r \t \v \ddd
(up to three octal digits) and \\.

Example:

message_reject_characters = \0

This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)
The maximal size in bytes of a message, including envelope information.

Note: be careful when making changes. Excessively small values will
result in the loss of non-delivery notifications, when a bounce message
size exceeds the local or remote MTA's message size limit.

message_strip_characters (default: empty)
The set of characters that Postfix will remove from message content.
The usual C-like escape sequences are recognized: \a \b \f \n \r \t \v
\ddd (up to three octal digits) and \\.

Example:

message_strip_characters = \0

This feature is available in Postfix 2.3 and later.

milter_command_timeout (default: 30s)
The time limit for sending an SMTP command to a Milter (mail filter)
application, and for receiving the response.

Specify a non-zero time value (an integral value plus an optional one-
letter suffix that specifies the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -d output)
The macros that are sent to Milter (mail filter) applications after
completion of an SMTP connection. See MILTER_README for a list of
available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)
The time limit for connecting to a Milter (mail filter) application,
and for negotiating protocol options.

Specify a non-zero time value (an integral value plus an optional one-
letter suffix that specifies the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)
The time limit for sending message content to a Milter (mail filter)
application, and for receiving the response.

Specify a non-zero time value (an integral value plus an optional one-
letter suffix that specifies the time unit).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -d output)
The macros that are sent to version 4 or higher Milter (mail filter)
applications after the SMTP DATA command. See MILTER_README for a list
of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)
The default action when a Milter (mail filter) application is unavail-
able or mis-configured. Specify one of the following:

accept Proceed as if the mail filter was not present.

reject Reject all further commands in this session with a permanent
status code.

tempfail
Reject all further commands in this session with a temporary
status code.

quarantine
Like "accept", but freeze the message in the "hold" queue.
Available with Postfix 2.6 and later.

This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -d output)
The macros that are sent to Milter (mail filter) applications after the
message end-of-data. See MILTER_README for a list of available macro
names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_end_of_header_macros (default: see postconf -d output)
The macros that are sent to Milter (mail filter) applications after the
end of the message header. See MILTER_README for a list of available
macro names and their meanings.

This feature is available in Postfix 2.5 and later.

milter_header_checks (default: empty)
Optional lookup tables for content inspection of message headers that
are produced by Milter applications. See the header_checks(5) manual
page available actions. Currently, PREPEND is not implemented.

The following example sends all mail that is marked as SPAM to a spam
handling machine. Note that matches are case-insensitive by default.

/etc/postfix/main.cf:
milter_header_checks = pcre:/etc/postfix/milter_header_checks

/etc/postfix/milter_header_checks:
/^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25

The milter_header_checks mechanism could also be used for whitelisting.
For example it could be used to skip heavy content inspection for DKIM-
signed mail from known friendly domains.

This feature is available in Postfix 2.7, and as an optional patch for
Postfix 2.6.

milter_helo_macros (default: see postconf -d output)
The macros that are sent to Milter (mail filter) applications after the
SMTP HELO or EHLO command. See MILTER_README for a list of available
macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)
The {daemon_name} macro value for Milter (mail filter) applications.
See MILTER_README for a list of available macro names and their mean-
ings.

This feature is available in Postfix 2.3 and later.

milter_macro_v (default: $mail_name $mail_version)
The {v} macro value for Milter (mail filter) applications. See MIL-
TER_README for a list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -d output)
The macros that are sent to Milter (mail filter) applications after the
SMTP MAIL FROM command. See MILTER_README for a list of available macro
names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_protocol (default: 6)
The mail filter protocol version and optional protocol extensions for
communication with a Milter application; prior to Postfix 2.6 the
default protocol is 2. Postfix sends this version number during the
initial protocol handshake. It should match the version number that is
expected by the mail filter application (or by its Milter library).

Protocol versions:

2 Use Sendmail 8 mail filter protocol version 2 (default with
Sendmail version 8.11 .. 8.13 and Postfix version 2.3 .. 2.5).

3 Use Sendmail 8 mail filter protocol version 3.

4 Use Sendmail 8 mail filter protocol version 4.

6 Use Sendmail 8 mail filter protocol version 6 (default with
Sendmail version 8.14 and Postfix version 2.6).

Protocol extensions:

no_header_reply
Specify this when the Milter application will not reply for each
individual message header.

This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -d output)
The macros that are sent to Milter (mail filter) applications after the
SMTP RCPT TO command. See MILTER_README for a list of available macro
names and their meanings.

This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -d output)
The macros that are sent to version 3 or higher Milter (mail filter)
applications after an unknown SMTP command. See MILTER_README for a
list of available macro names and their meanings.

This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)
The maximal length of MIME multipart boundary strings. The MIME proces-
sor is unable to distinguish between boundary strings that do not dif-
fer in the first $mime_boundary_length_limit characters.

This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)
Optional lookup tables for content inspection of MIME related message
headers, as described in the header_checks(5) manual page.

This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)
The maximal recursion level that the MIME processor will handle. Post-
fix refuses mail that is nested deeper than the specified limit.

This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)
The minimal time between attempts to deliver a deferred message; prior
to Postfix 2.4 the default value was 1000s.

This parameter also limits the time an unreachable destination is kept
in the short-term, in-memory, destination status cache.

This parameter should be set greater than or equal to $queue_run_delay.
See also $maximal_backoff_time.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

multi_instance_directories (default: empty)
An optional list of non-default Postfix configuration directories;
these directories belong to additional Postfix instances that share the
Postfix executable files and documentation with the default Postfix
instance, and that are started, stopped, etc., together with the
default Postfix instance. Specify a list of pathnames separated by
comma or whitespace.

When $multi_instance_directories is empty, the postfix(1) command runs
in single-instance mode and operates on a single Postfix instance only.
Otherwise, the postfix(1) command runs in multi-instance mode and
invokes the multi-instance manager specified with the
multi_instance_wrapper parameter. The multi-instance manager in turn
executes postfix(1) commands for the default instance and for all Post-
fix instances in $multi_instance_directories.

Currently, this parameter setting is ignored except for the default
main.cf file.

This feature is available in Postfix 2.6 and later.

multi_instance_enable (default: no)
Allow this Postfix instance to be started, stopped, etc., by a multi-
instance manager. By default, new instances are created in a safe
state that prevents them from being started inadvertently. This param-
eter is reserved for the multi-instance manager.

This feature is available in Postfix 2.6 and later.

multi_instance_group (default: empty)
The optional instance group name of this Postfix instance. A group
identifies closely-related Postfix instances that the multi-instance
manager can start, stop, etc., as a unit. This parameter is reserved
for the multi-instance manager.

This feature is available in Postfix 2.6 and later.

multi_instance_name (default: empty)
The optional instance name of this Postfix instance. This name becomes
also the default value for the syslog_name parameter.

This feature is available in Postfix 2.6 and later.

multi_instance_wrapper (default: empty)
The pathname of a multi-instance manager command that the postfix(1)
command invokes when the multi_instance_directories parameter value is
non-empty. The pathname may be followed by initial command arguments
separated by whitespace; shell metacharacters such as quotes are not
supported in this context.

The postfix(1) command invokes the manager command with the postfix(1)
non-option command arguments on the manager command line, and with all
installation configuration parameters exported into the manager command
process environment. The manager command in turn invokes the postfix(1)
command for individual Postfix instances as "postfix -c config_direc-
tory command".

This feature is available in Postfix 2.6 and later.

multi_recipient_bounce_reject_code (default: 550)
The numerical Postfix SMTP server response code when a remote SMTP
client request is blocked by the reject_multi_recipient_bounce restric-
tion.

Do not change this unless you have a complete understanding of RFC
2821.

This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)
The list of domains that are delivered via the $local_transport mail
delivery transport. By default this is the Postfix local(8) delivery
agent which looks up all recipients in /etc/passwd and /etc/aliases.
The SMTP server validates recipient addresses with $local_recipi-
ent_maps and rejects non-existent recipients. See also the local domain
class in the ADDRESS_CLASS_README file.

The default mydestination value specifies names for the local machine
only. On a mail domain gateway, you should also include $mydomain.

The $local_transport delivery method is also selected for mail
addressed to user@[the.net.work.address] of the mail system (the IP
addresses specified with the inet_interfaces and proxy_interfaces
parameters).

Warnings:

· Do not specify the names of virtual domains - those domains are
specified elsewhere. See VIRTUAL_README for more information.

· Do not specify the names of domains that this machine is backup
MX host for. See STANDARD_CONFIGURATION_README for how to set up
backup MX hosts.

· By default, the Postfix SMTP server rejects mail for recipients
not listed with the local_recipient_maps parameter. See the
postconf(5) manual for a description of the local_recipient_maps
and unknown_local_recipient_reject_code parameters.

Examples:

mydestination = $myhostname, localhost.$mydomain $mydomain
mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)
The internet domain name of this mail system. The default is to use
$myhostname minus the first component. $mydomain is used as a default
value for many other configuration parameters.

Example:

mydomain = domain.tld

myhostname (default: see postconf -d output)
The internet hostname of this mail system. The default is to use the
fully-qualified domain name from gethostname(). $myhostname is used as
a default value for many other configuration parameters.

Example:

myhostname = host.example.com

mynetworks (default: see postconf -d output)
The list of "trusted" SMTP clients that have more privileges than
"strangers".

In particular, "trusted" SMTP clients are allowed to relay mail through
Postfix. See the smtpd_recipient_restrictions parameter description in
the postconf(5) manual.

You can specify the list of "trusted" network addresses by hand or you
can let Postfix do it for you (which is the default). See the descrip-
tion of the mynetworks_style parameter for more information.

If you specify the mynetworks list by hand, Postfix ignores the mynet-
works_style setting.

Specify a list of network addresses or network/netmask patterns, sepa-
rated by commas and/or whitespace. Continue long lines by starting the
next line with whitespace.

The netmask specifies the number of bits in the network part of a host
address. You can also specify "/file/name" or "type:table" patterns.
A "/file/name" pattern is replaced by its contents; a "type:table"
lookup table is matched when a table entry matches a lookup string (the
lookup result is ignored).

The list is matched left to right, and the search stops on the first
match. Specify "!pattern" to exclude an address or network block from
the list. The form "!/file/name" is supported only in Postfix version
2.4 and later.

Note: IP version 6 address information must be specified inside [] in
the mynetworks value, and in files specified with "/file/name". IP
version 6 addresses contain the ":" character, and would otherwise be
confused with a "type:table" pattern.

Examples:

mynetworks = 127.0.0.0/8 168.100.189.0/28
mynetworks = !192.168.0.1, 192.168.0.0/28
mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
mynetworks = $config_directory/mynetworks
mynetworks = hash:/etc/postfix/network_table

mynetworks_style (default: subnet)
The method to generate the default value for the mynetworks parameter.
This is the list of trusted networks for relay access control etc.

· Specify "mynetworks_style = host" when Postfix should "trust"
only the local machine.

· Specify "mynetworks_style = subnet" when Postfix should "trust"
SMTP clients in the same IP subnetworks as the local machine.
On Linux, this works correctly only with interfaces specified
with the "ifconfig" command.

· Specify "mynetworks_style = class" when Postfix should "trust"
SMTP clients in the same IP class A/B/C networks as the local
machine. Don't do this with a dialup site - it would cause
Postfix to "trust" your entire provider's network. Instead,
specify an explicit mynetworks list by hand, as described with
the mynetworks configuration parameter.

myorigin (default: $myhostname)
The domain name that locally-posted mail appears to come from, and that
locally posted mail is delivered to. The default, $myhostname, is ade-
quate for small sites. If you run a domain with multiple machines, you
should (1) change this to $mydomain and (2) set up a domain-wide alias
database that aliases each user to user@that.users.mailhost.

Example:

myorigin = $mydomain

nested_header_checks (default: $header_checks)
Optional lookup tables for content inspection of non-MIME message head-
ers in attached messages, as described in the header_checks(5) manual
page.

This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)
Sendmail compatibility feature that specifies the location of the
newaliases(1) command. This command can be used to rebuild the local(8)
aliases(5) database.

non_fqdn_reject_code (default: 504)
The numerical Postfix SMTP server reply code when a client request is
rejected by the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender
or reject_non_fqdn_recipient restriction.

non_smtpd_milters (default: empty)
A list of Milter (mail filter) applications for new mail that does not
arrive via the Postfix smtpd(8) server. This includes local submission
via the sendmail(1) command line, new mail that arrives via the Postfix
qmqpd(8) server, and old mail that is re-injected into the queue with
"postsuper -r". See the MILTER_README document for details.

This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)
The list of error classes that are reported to the postmaster. The
default is to report only the most serious problems. The paranoid may
wish to turn on the policy (UCE and mail relaying) and protocol error
(broken mail software) reports.

NOTE: postmaster notifications may contain confidential information
such as SASL passwords or message content. It is the system adminis-
trator's responsibility to treat such information with care.

The error classes are:

bounce (also implies 2bounce)
Send the postmaster copies of the headers of bounced mail, and
send transcripts of SMTP sessions when Postfix rejects mail. The
notification is sent to the address specified with the
bounce_notice_recipient configuration parameter (default: post-
master).

2bounce
Send undeliverable bounced mail to the postmaster. The notifica-
tion is sent to the address specified with the
2bounce_notice_recipient configuration parameter (default: post-
master).

delay Send the postmaster copies of the headers of delayed mail. The
notification is sent to the address specified with the
delay_notice_recipient configuration parameter (default: post-
master).

policy Send the postmaster a transcript of the SMTP session when a
client request was rejected because of (UCE) policy. The notifi-
cation is sent to the address specified with the
error_notice_recipient configuration parameter (default: post-
master).

protocol
Send the postmaster a transcript of the SMTP session in case of
client or server protocol errors. The notification is sent to
the address specified with the error_notice_recipient configura-
tion parameter (default: postmaster).

resource
Inform the postmaster of mail not delivered due to resource
problems. The notification is sent to the address specified
with the error_notice_recipient configuration parameter
(default: postmaster).

software
Inform the postmaster of mail not delivered due to software
problems. The notification is sent to the address specified
with the error_notice_recipient configuration parameter
(default: postmaster).

Examples:

notify_classes = bounce, delay, policy, protocol, resource, software
notify_classes = 2bounce, resource, software

owner_request_special (default: yes)
Give special treatment to owner-listname and listname-request address
localparts: don't split such addresses when the recipient_delimiter is
set to "-". This feature is useful for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)
What Postfix features match subdomains of "domain.tld" automatically,
instead of requiring an explicit ".domain.tld" pattern. This is
planned backwards compatibility: eventually, all Postfix features are
expected to require explicit ".domain.tld" style patterns when you
really want to match subdomains.

permit_mx_backup_networks (default: empty)
Restrict the use of the permit_mx_backup SMTP access feature to only
domains whose primary MX hosts match the listed networks. The parame-
ter value syntax is the same as with the mynetworks parameter; note,
however, that the default value is empty.

pickup_service_name (default: pickup)
The name of the pickup(8) service. This service picks up local mail
submissions from the Postfix maildrop queue.

This feature is available in Postfix 2.0 and later.

plaintext_reject_code (default: 450)
The numerical Postfix SMTP server response code when a request is
rejected by the reject_plaintext_session restriction.

This feature is available in Postfix 2.3 and later.

postmulti_control_commands (default: reload flush)
The postfix(1) commands that the postmulti(1) instance manager treats
as "control" commands, that operate on running instances. For these
commands, disabled instances are skipped.

This feature is available in Postfix 2.6 and later.

postmulti_start_commands (default: start)
The postfix(1) commands that the postmulti(1) instance manager treats
as "start" commands. For these commands, disabled instances are
"checked" rather than "started", and failure to "start" a member
instance of an instance group will abort the start-up of later
instances.

This feature is available in Postfix 2.6 and later.

postmulti_stop_commands (default: see postconf -d output)
The postfix(1) commands that the postmulti(1) instance manager treats
as "stop" commands. For these commands, disabled instances are skipped,
and enabled instances are processed in reverse order.

This feature is available in Postfix 2.6 and later.

prepend_delivered_header (default: command, file, forward)
The message delivery contexts where the Postfix local(8) delivery agent
prepends a Delivered-To: message header with the address that the mail
was delivered to. This information is used for mail delivery loop
detection.

By default, the Postfix local delivery agent prepends a Delivered-To:
header when forwarding mail and when delivering to file (mailbox) and
command. Turning off the Delivered-To: header when forwarding mail is
not recommended.

Specify zero or more of forward, file, or command.

Example:

prepend_delivered_header = forward

process_id (read-only)
The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)
The location of Postfix PID files relative to $queue_directory. This
is a read-only parameter.

process_name (read-only)
The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)
What address lookup tables copy an address extension from the lookup
key to the lookup result.

For example, with a virtual(5) mapping of "joe@example.com =>
joe.user@example.net", the address "joe+foo@example.com" would rewrite
to "joe.user+foo@example.net".

Specify zero or more of canonical, virtual, alias, forward, include or
generic. These cause address extension propagation with canonical(5),
virtual(5), and aliases(5) maps, with local(8) .forward and :include:
file lookups, and with smtp(8) generic maps, respectively.

Note: enabling this feature for types other than canonical and virtual
is likely to cause problems when mail is forwarded to other sites,
especially with mail that is sent to a mailing list exploder address.

Examples:

propagate_unmatched_extensions = canonical, virtual, alias,
forward, include
propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)
The network interface addresses that this mail system receives mail on
by way of a proxy or network address translation unit.

This feature is available in Postfix 2.0 and later.

You must specify your "outside" proxy/NAT addresses when your system is
a backup MX host for other domains, otherwise mail delivery loops will
happen when the primary MX host is down.

Example:

proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)
The lookup tables that the proxymap(8) server is allowed to access for
the read-only service. Table references that don't begin with proxy:
are ignored.

This feature is available in Postfix 2.0 and later.

proxy_write_maps (default: see postconf -d output)
The lookup tables that the proxymap(8) server is allowed to access for
the read-write service. Postfix-owned local database files should be
stored under the Postfix-owned data_directory. Table references that
don't begin with proxy: are ignored.

This feature is available in Postfix 2.5 and later.

proxymap_service_name (default: proxymap)
The name of the proxymap read-only table lookup service. This service
is normally implemented by the proxymap(8) daemon.

This feature is available in Postfix 2.6 and later.

proxywrite_service_name (default: proxywrite)
The name of the proxywrite read-write table lookup service. This ser-
vice is normally implemented by the proxymap(8) daemon.

This feature is available in Postfix 2.6 and later.

qmgr_clog_warn_time (default: 300s)
The minimal delay between warnings that a specific destination is clog-
ging up the Postfix active queue. Specify 0 to disable.

This feature is enabled with the helpful_warnings parameter.

This feature is available in Postfix 2.0 and later.

qmgr_fudge_factor (default: 100)
Obsolete feature: the percentage of delivery resources that a busy mail
system will use up for delivery of a large mailing list message.

This feature exists only in the oqmgr(8) old queue manager. The current
queue manager solves the problem in a better way.

qmgr_message_active_limit (default: 20000)
The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)
The maximal number of recipients held in memory by the Postfix queue
manager, and the maximal size of the size of the short-term, in-memory
"dead" destination status cache.

qmgr_message_recipient_minimum (default: 10)
The minimal number of in-memory recipients for any message. This takes
priority over any other in-memory recipient limits (i.e., the global
qmgr_message_recipient_limit and the per transport _recipient_limit) if
necessary. The minimum value allowed for this parameter is 1.

qmqpd_authorized_clients (default: empty)
What clients are allowed to connect to the QMQP server port.

By default, no client is allowed to use the service. This is because
the QMQP server will relay mail to any destination.

Specify a list of client patterns. A list pattern specifies a host
name, a domain name, an internet address, or a network/mask pattern,
where the mask specifies the number of bits in the network part. When
a pattern specifies a file name, its contents are substituted for the
file name; when a pattern is a "type:table" table specification, table
lookup is used instead.

Patterns are separated by whitespace and/or commas. In order to reverse
the result, precede a pattern with an exclamation point (!). The form
"!/file/name" is supported only in Postfix version 2.4 and later.

Example:

qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_client_port_logging (default: no)
Enable logging of the remote QMQP client port in addition to the host-
name and IP address. The logging format is "host[address]:port".

This feature is available in Postfix 2.5 and later.

qmqpd_error_delay (default: 1s)
How long the QMQP server will pause before sending a negative reply to
the client. The purpose is to slow down confused or malicious clients.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

qmqpd_timeout (default: 300s)
The time limit for sending or receiving information over the network.
If a read or write operation blocks for more than $qmqpd_timeout sec-
onds the QMQP server gives up and disconnects.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

queue_directory (default: see postconf -d output)
The location of the Postfix top-level queue directory. This is the root
directory of Postfix daemon processes that run chrooted.

queue_file_attribute_count_limit (default: 100)
The maximal number of (name=value) attributes that may be stored in a
Postfix queue file. The limit is enforced by the cleanup(8) server.

This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)
The minimal amount of free space in bytes in the queue file system that
is needed to receive mail. This is currently used by the SMTP server
to decide if it will accept any mail at all.

By default, the Postfix SMTP server rejects MAIL FROM commands when the
amount of free space is less than 1.5*$message_size_limit (Postfix ver-
sion 2.1 and later). To specify a higher minimum free space limit,
specify a queue_minfree value that is at least 1.5*$message_size_limit.

With Postfix versions 2.0 and earlier, a queue_minfree value of zero
means there is no minimum required amount of free space.

queue_run_delay (default: 300s)
The time between deferred queue scans by the queue manager; prior to
Postfix 2.4 the default value was 1000s.

This parameter should be set less than or equal to $minimal_back-
off_time. See also $maximal_backoff_time.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

queue_service_name (default: qmgr)
The name of the qmgr(8) service. This service manages the Postfix queue
and schedules delivery requests.

This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)
Optional lookup tables with RBL response templates. The tables are
indexed by the RBL domain name. By default, Postfix uses the default
template as specified with the default_rbl_reply configuration parame-
ter. See there for a discussion of the syntax of RBL reply templates.

This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)
The location of Postfix README files that describe how to build, con-
figure or operate a specific Postfix subsystem or feature.

receive_override_options (default: empty)
Enable or disable recipient validation, built-in content filtering, or
address mapping. Typically, these are specified in master.cf as com-
mand-line arguments for the smtpd(8), qmqpd(8) or pickup(8) daemons.

Specify zero or more of the following options. The options override
main.cf settings and are either implemented by smtpd(8), qmqpd(8), or
pickup(8) themselves, or they are forwarded to the cleanup server.

no_unknown_recipient_checks
Do not try to reject unknown recipients (SMTP server only).
This is typically specified AFTER an external content filter.

no_address_mappings
Disable canonical address mapping, virtual alias map expansion,
address masquerading, and automatic BCC (blind carbon-copy)
recipients. This is typically specified BEFORE an external con-
tent filter.

no_header_body_checks
Disable header/body_checks. This is typically specified AFTER an
external content filter.

no_milters
Disable Milter (mail filter) applications. This is typically
specified AFTER an external content filter.

Note: when the "BEFORE content filter" receive_override_options setting
is specified in the main.cf file, specify the "AFTER content filter"
receive_override_options setting in master.cf (and vice versa).

Examples:

receive_override_options =
no_unknown_recipient_checks, no_header_body_checks
receive_override_options = no_address_mappings

This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)
Optional BCC (blind carbon-copy) address lookup tables, indexed by
recipient address. The BCC address (multiple results are not sup-
ported) is added when mail enters from outside of Postfix.

This feature is available in Postfix 2.1 and later.

The table search order is as follows:

· Look up the "user+extension@domain.tld" address including the
optional address extension.

· Look up the "user@domain.tld" address without the optional
address extension.

· Look up the "user+extension" address local part when the recipi-
ent domain equals $myorigin, $mydestination, $inet_interfaces or
$proxy_interfaces.

· Look up the "user" address local part when the recipient domain
equals $myorigin, $mydestination, $inet_interfaces or
$proxy_interfaces.

· Look up the "@domain.tld" part.

Specify the types and names of databases to use. After change, run
"postmap /etc/postfix/recipient_bcc".

Note: if mail to the BCC address bounces it will be returned to the
sender.

Example:

recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

recipient_canonical_classes (default: envelope_recipient, header_recipient)
What addresses are subject to recipient_canonical_maps address mapping.
By default, recipient_canonical_maps address mapping is applied to
envelope recipient addresses, and to header recipient addresses.

Specify one or more of: envelope_recipient, header_recipient

This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)
Optional address mapping lookup tables for envelope and header recipi-
ent addresses. The table format and lookups are documented in canoni-
cal(5).

Note: $recipient_canonical_maps is processed before $canonical_maps.

Example:

recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

recipient_delimiter (default: empty)
The separator between user names and address extensions (user+foo).
See canonical(5), local(8), relocated(5) and virtual(5) for the effects
this has on aliases, canonical, virtual, relocated and on .forward file
lookups. Basically, the software tries user+foo and .forward+foo
before trying user and .forward.

Example:

recipient_delimiter = +

reject_code (default: 554)
The numerical Postfix SMTP server response code when a remote SMTP
client request is rejected by the "reject" restriction.

Do not change this unless you have a complete understanding of RFC
2821.

reject_tempfail_action (default: defer_if_permit)
The Postfix SMTP server's action when a reject-type restriction fails
due to a temporary error condition. Specify "defer" to defer the remote
SMTP client request immediately. With the default "defer_if_permit"
action, the Postfix SMTP server continues to look for opportunities to
reject mail, and defers the client request only if it would otherwise
be accepted.

For finer control, see: unverified_recipient_tempfail_action, unveri-
fied_sender_tempfail_action, unknown_address_tempfail_action, and
unknown_helo_hostname_tempfail_action.

This feature is available in Postfix 2.6 and later.

relay_clientcerts (default: empty)
List of tables with remote SMTP client-certificate fingerprints for
which the Postfix SMTP server will allow access with the per-
mit_tls_clientcerts feature. The fingerprint digest algorithm is con-
figurable via the smtpd_tls_fingerprint_digest parameter (hard-coded as
md5 prior to Postfix version 2.5).

Postfix lookup tables are in the form of (key, value) pairs. Since we
only need the key, the value can be chosen freely, e.g. the name of
the user or host: D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80
lutzpc.at.home

Example:

relay_clientcerts = hash:/etc/postfix/relay_clientcerts

For more fine-grained control, use check_ccert_access to select an
appropriate access(5) policy for each client. See RESTRIC-
TION_CLASS_README.

This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit (default: $default_destination_concur-
rency_limit)
The maximal number of parallel deliveries to the same destination via
the relay message delivery transport. This limit is enforced by the
queue manager. The message delivery transport name is the first field
in the entry in the master.cf file.

This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit (default: $default_destination_recipi-
ent_limit)
The maximal number of recipients per message for the relay message
delivery transport. This limit is enforced by the queue manager. The
message delivery transport name is the first field in the entry in the
master.cf file.

Setting this parameter to a value of 1 changes the meaning of
relay_destination_concurrency_limit from concurrency per domain into
concurrency per recipient.

This feature is available in Postfix 2.0 and later.

relay_domains (default: $mydestination)
What destination domains (and subdomains thereof) this system will
relay mail to. Subdomain matching is controlled with the par-
ent_domain_matches_subdomains parameter. For details about how the
relay_domains value is used, see the description of the per-
mit_auth_destination and reject_unauth_destination SMTP recipient
restrictions.

Domains that match $relay_domains are delivered with the $relay_trans-
port mail delivery transport. The SMTP server validates recipient
addresses with $relay_recipient_maps and rejects non-existent recipi-
ents. See also the relay domains address class in the
ADDRESS_CLASS_README file.

Note: Postfix will not automatically forward mail for domains that list
this system as their primary or backup MX host. See the per-
mit_mx_backup restriction in the postconf(5) manual page.

Specify a list of host or domain names, "/file/name" patterns or
"type:table" lookup tables, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace. A
"/file/name" pattern is replaced by its contents; a "type:table" lookup
table is matched when a (parent) domain appears as lookup key. Specify
"!pattern" to exclude a domain from the list. The form "!/file/name" is
supported only in Postfix version 2.4 and later.

relay_domains_reject_code (default: 554)
The numerical Postfix SMTP server response code when a client request
is rejected by the reject_unauth_destination recipient restriction.

Do not change this unless you have a complete understanding of RFC
2821.

relay_recipient_maps (default: empty)
Optional lookup tables with all valid addresses in the domains that
match $relay_domains. Specify @domain as a wild-card for domains that
have no valid recipient list, and become a source of backscatter mail:
Postfix accepts spam for non-existent recipients and then floods inno-
cent people with undeliverable mail. Technically, tables listed with
$relay_recipient_maps are used as lists: Postfix needs to know only if
a lookup string is found or not, but it does not use the result from
table lookup.

If this parameter is non-empty, then the Postfix SMTP server will
reject mail to unknown relay users. This feature is off by default.

See also the relay domains address class in the ADDRESS_CLASS_README
file.

Example:

relay_recipient_maps = hash:/etc/postfix/relay_recipients

This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)
The default mail delivery transport and next-hop destination for remote
delivery to domains listed with $relay_domains. In order of decreasing
precedence, the nexthop destination is taken from $relay_transport,
$sender_dependent_relayhost_maps, $relayhost, or from the recipient
domain. This information can be overruled with the transport(5) table.

See also the relay domains address class in the ADDRESS_CLASS_README
file.

This feature is available in Postfix 2.0 and later.

relayhost (default: empty)
The next-hop destination of non-local mail; overrides non-local domains
in recipient addresses. This information is overruled with relay_trans-
port, sender_dependent_default_transport_maps, default_transport,
sender_dependent_relayhost_maps and with the transport(5) table.

On an intranet, specify the organizational domain name. If your inter-
nal DNS uses no MX records, specify the name of the intranet gateway
host instead.

In the case of SMTP, specify a domain name, hostname, hostname:port,
[hostname]:port, [hostaddress] or [hostaddress]:port. The form [host-
name] turns off MX lookups.

If you're connected via UUCP, see the UUCP_README file for useful
information.

Examples:

relayhost = $mydomain
relayhost = [gateway.example.com]
relayhost = uucphost
relayhost = [an.ip.add.ress]

relocated_maps (default: empty)
Optional lookup tables with new contact information for users or
domains that no longer exist. The table format and lookups are docu-
mented in relocated(5).

If you use this feature, run "postmap /etc/postfix/relocated" to build
the necessary DBM or DB file after change, then "postfix reload" to
make the changes visible.

Examples:

relocated_maps = dbm:/etc/postfix/relocated
relocated_maps = hash:/etc/postfix/relocated

remote_header_rewrite_domain (default: empty)
Don't rewrite message headers from remote clients at all when this
parameter is empty; otherwise, rewrite message headers and append the
specified domain name to incomplete addresses. The local_header_re-
write_clients parameter controls what clients Postfix considers local.

Examples:

The safe setting: append "domain.invalid" to incomplete header
addresses from remote SMTP clients, so that those addresses cannot be
confused with local addresses.

remote_header_rewrite_domain = domain.invalid

The default, purist, setting: don't rewrite headers from remote clients
at all.

remote_header_rewrite_domain =

require_home_directory (default: no)
Require that a local(8) recipient's home directory exists before mail
delivery is attempted. By default this test is disabled. It can be
useful for environments that import home directories to the mail server
(IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).

resolve_dequoted_address (default: yes)
Resolve a recipient address safely instead of correctly, by looking
inside quotes.

By default, the Postfix address resolver does not quote the address
localpart as per RFC 822, so that additional @ or % or ! operators
remain visible. This behavior is safe but it is also technically incor-
rect.

If you specify "resolve_dequoted_address = no", then the Postfix
resolver will not know about additional @ etc. operators in the address
localpart. This opens opportunities for obscure mail relay attacks with
user@domain@domain addresses when Postfix provides backup MX service
for Sendmail systems.

resolve_null_domain (default: no)
Resolve an address that ends in the "@" null domain as if the local
hostname were specified, instead of rejecting the address as invalid.

This feature is available in Postfix 2.1 and later. Earlier versions
always resolve the null domain as the local hostname.

The Postfix SMTP server uses this feature to reject mail from or to
addresses that end in the "@" null domain, and from addresses that re-
write into a form that ends in the "@" null domain.

resolve_numeric_domain (default: no)
Resolve "user@ipaddress" as "user@[ipaddress]", instead of rejecting
the address as invalid.

This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)
The name of the address rewriting service. This service rewrites
addresses to standard form and resolves them to a (delivery method,
next-hop host, recipient) triple.

This feature is available in Postfix 2.0 and later.

sample_directory (default: /etc/postfix)
The name of the directory with example Postfix configuration files.
Starting with Postfix 2.1, these files have been replaced with the
postconf(5) manual page.

send_cyrus_sasl_authzid (default: no)
When authenticating to a remote SMTP or LMTP server with the default
setting "no", send no SASL authoriZation ID (authzid); send only the
SASL authentiCation ID (authcid) plus the authcid's password.

The non-default setting "yes" enables the behavior of older Postfix
versions. These always send a SASL authzid that is equal to the SASL
authcid, but this causes inter-operability problems with some SMTP
servers.

This feature is available in Postfix 2.4.4 and later.

sender_based_routing (default: no)
This parameter should not be used. It was replaced by sender_depen-
dent_relayhost_maps in Postfix version 2.3.

sender_bcc_maps (default: empty)
Optional BCC (blind carbon-copy) address lookup tables, indexed by
sender address. The BCC address (multiple results are not supported)
is added when mail enters from outside of Postfix.

This feature is available in Postfix 2.1 and later.

The table search order is as follows:

· Look up the "user+extension@domain.tld" address including the
optional address extension.

· Look up the "user@domain.tld" address without the optional
address extension.

· Look up the "user+extension" address local part when the sender
domain equals $myorigin, $mydestination, $inet_interfaces or
$proxy_interfaces.

· Look up the "user" address local part when the sender domain
equals $myorigin, $mydestination, $inet_interfaces or
$proxy_interfaces.

· Look up the "@domain.tld" part.

Specify the types and names of databases to use. After change, run
"postmap /etc/postfix/sender_bcc".

Note: if mail to the BCC address bounces it will be returned to the
sender.

Example:

sender_bcc_maps = hash:/etc/postfix/sender_bcc

sender_canonical_classes (default: envelope_sender, header_sender)
What addresses are subject to sender_canonical_maps address mapping.
By default, sender_canonical_maps address mapping is applied to enve-
lope sender addresses, and to header sender addresses.

Specify one or more of: envelope_sender, header_sender

This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)
Optional address mapping lookup tables for envelope and header sender
addresses. The table format and lookups are documented in canoni-
cal(5).

Example: you want to rewrite the SENDER address "user@ugly.domain" to
"user@pretty.domain", while still being able to send mail to the RECIP-
IENT address "user@ugly.domain".

Note: $sender_canonical_maps is processed before $canonical_maps.

Example:

sender_canonical_maps = hash:/etc/postfix/sender_canonical

sender_dependent_default_transport_maps (default: empty)
A sender-dependent override for the global default_transport parameter
setting. The tables are searched by the envelope sender address and
@domain. A lookup result of DUNNO terminates the search without over-
riding the global default_transport parameter setting. This informa-
tion is overruled with the transport(5) table.

Note: this overrides default_transport, not transport_maps, and there-
fore the expected syntax is that of default_transport, not the syntax
of transport_maps. Specifically, this does not support the trans-
port_maps syntax for null transport, null nexthop, or null email
addresses.

For safety reasons, this feature does not allow $number substitutions
in regular expression maps.

This feature is available in Postfix 2.7 and later.

sender_dependent_relayhost_maps (default: empty)
A sender-dependent override for the global relayhost parameter setting.
The tables are searched by the envelope sender address and @domain. A
lookup result of DUNNO terminates the search without overriding the
global relayhost parameter setting (Postfix 2.6 and later). This infor-
mation is overruled with relay_transport, sender_depen-
dent_default_transport_maps, default_transport and with the trans-
port(5) table.

For safety reasons, this feature does not allow $number substitutions
in regular expression maps.

This feature is available in Postfix 2.3 and later.

sendmail_path (default: see postconf -d output)
A Sendmail compatibility feature that specifies the location of the
Postfix sendmail(1) command. This command can be used to submit mail
into the Postfix queue.

service_throttle_time (default: 60s)
How long the Postfix master(8) waits before forking a server that
appears to be malfunctioning.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

setgid_group (default: postdrop)
The group ownership of set-gid Postfix commands and of group-writable
Postfix directories. When this parameter value is changed you need to
re-run "postfix set-permissions" (with Postfix version 2.0 and earlier:
"/etc/postfix/post-install set-permissions".

show_user_unknown_table_name (default: yes)
Display the name of the recipient table in the "User unknown"
responses. The extra detail makes trouble shooting easier but also
reveals information that is nobody elses business.

This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)
The name of the showq(8) service. This service produces mail queue sta-
tus reports.

This feature is available in Postfix 2.0 and later.

smtp_always_send_ehlo (default: yes)
Always send EHLO at the start of an SMTP session.

With "smtp_always_send_ehlo = no", Postfix sends EHLO only when the
word "ESMTP" appears in the server greeting banner (example: 220
spike.porcupine.org ESMTP Postfix).

smtp_bind_address (default: empty)
An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv4 connection.

This can be specified in the main.cf file for all SMTP clients, or it
can be specified in the master.cf file for a specific client, for exam-
ple:

/etc/postfix/master.cf:
smtp ... smtp -o smtp_bind_address=11.22.33.44

Note 1: when inet_interfaces specifies no more than one IPv4 address,
and that address is a non-loopback address, it is automatically used as
the smtp_bind_address. This supports virtual IP hosting, but can be a
problem on multi-homed firewalls. See the inet_interfaces documentation
for more detail.

Note 2: address information may be enclosed inside [], but this form is
not required here.

smtp_bind_address6 (default: empty)
An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv6 connection.

This feature is available in Postfix 2.2 and later.

This can be specified in the main.cf file for all SMTP clients, or it
can be specified in the master.cf file for a specific client, for exam-
ple:

/etc/postfix/master.cf:
smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

Note 1: when inet_interfaces specifies no more than one IPv6 address,
and that address is a non-loopback address, it is automatically used as
the smtp_bind_address6. This supports virtual IP hosting, but can be a
problem on multi-homed firewalls. See the inet_interfaces documentation
for more detail.

Note 2: address information may be enclosed inside [], but this form is
not recommended here.

smtp_body_checks (default: empty)
Restricted body_checks(5) tables for the Postfix SMTP client. These
tables are searched while mail is being delivered. Actions that change
the delivery time or destination are not available.

This feature is available in Postfix 2.5 and later.

smtp_cname_overrides_servername (default: version dependent)
Allow DNS CNAME records to override the servername that the Postfix
SMTP client uses for logging, SASL password lookup, TLS policy deci-
sions, or TLS certificate verification. The value "no" hardens Postfix
smtp_tls_per_site hostname-based policies against false hostname infor-
mation in DNS CNAME records, and makes SASL password file lookups more
predictable. This is the default setting as of Postfix 2.3.

This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
The SMTP client time limit for completing a TCP connection, or zero
(use the operating system built-in time limit).

When no connection can be made within the deadline, the Postfix SMTP
client tries the next address on the mail exchanger list. Specify 0 to
disable the time limit (i.e. use whatever timeout is implemented by the
operating system).

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_connection_cache_destinations (default: empty)
Permanently enable SMTP connection caching for the specified destina-
tions. With SMTP connection caching, a connection is not closed imme-
diately after completion of a mail transaction. Instead, the connec-
tion is kept open for up to $smtp_connection_cache_time_limit seconds.
This allows connections to be reused for other deliveries, and can
improve mail delivery performance.

Specify a comma or white space separated list of destinations or
pseudo-destinations:

· if mail is sent without a relay host: a domain name (the right-
hand side of an email address, without the [] around a numeric
IP address),

· if mail is sent via a relay host: a relay host name (without []
or non-default TCP port), as specified in main.cf or in the
transport map,

· if mail is sent via a UNIX-domain socket: a pathname (without
the unix: prefix),

· a /file/name with domain names and/or relay host names as
defined above,

· a "type:table" with domain names and/or relay host names on the
left-hand side. The right-hand side result from "type:table"
lookups is ignored.

This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)
Temporarily enable SMTP connection caching while a destination has a
high volume of mail in the active queue. With SMTP connection caching,
a connection is not closed immediately after completion of a mail
transaction. Instead, the connection is kept open for up to $smtp_con-
nection_cache_time_limit seconds. This allows connections to be reused
for other deliveries, and can improve mail delivery performance.

This feature is available in Postfix 2.2 and later.

smtp_connection_cache_reuse_limit (default: 10)
When SMTP connection caching is enabled, the number of times that an
SMTP session may be reused before it is closed.

This feature is available in Postfix 2.2. In Postfix 2.3 it is replaced
by $smtp_connection_reuse_time_limit.

smtp_connection_cache_time_limit (default: 2s)
When SMTP connection caching is enabled, the amount of time that an
unused SMTP client socket is kept open before it is closed. Do not
specify larger values without permission from the remote sites.

This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_time_limit (default: 300s)
The amount of time during which Postfix will use an SMTP connection
repeatedly. The timer starts when the connection is initiated (i.e. it
includes the connect, greeting and helo latency, in addition to the
latencies of subsequent mail delivery transactions).

This feature addresses a performance stability problem with remote SMTP
servers. This problem is not specific to Postfix: it can happen when
any MTA sends large amounts of SMTP email to a site that has multiple
MX hosts.

The problem starts when one of a set of MX hosts becomes slower than
the rest. Even though SMTP clients connect to fast and slow MX hosts
with equal probability, the slow MX host ends up with more simultaneous
inbound connections than the faster MX hosts, because the slow MX host
needs more time to serve each client request.

The slow MX host becomes a connection attractor. If one MX host
becomes N times slower than the rest, it dominates mail delivery
latency unless there are more than N fast MX hosts to counter the
effect. And if the number of MX hosts is smaller than N, the mail
delivery latency becomes effectively that of the slowest MX host
divided by the total number of MX hosts.

The solution uses connection caching in a way that differs from Postfix
version 2.2. By limiting the amount of time during which a connection
can be used repeatedly (instead of limiting the number of deliveries
over that connection), Postfix not only restores fairness in the dis-
tribution of simultaneous connections across a set of MX hosts, it also
favors deliveries over connections that perform well, which is exactly
what we want.

The default reuse time limit, 300s, is comparable to the various smtp
transaction timeouts which are fair estimates of maximum excess latency
for a slow delivery. Note that hosts may accept thousands of messages
over a single connection within the default connection reuse time
limit. This number is much larger than the default Postfix version 2.2
limit of 10 messages per cached connection. It may prove necessary to
lower the limit to avoid interoperability issues with MTAs that exhibit
bugs when many messages are delivered via a single connection. A lower
reuse time limit risks losing the benefit of connection reuse when the
average connection and mail delivery latency exceeds the reuse time
limit.

This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)
The SMTP client time limit for sending the SMTP ".", and for receiving
the server response.

When no response is received within the deadline, a warning is logged
that the mail may be delivered multiple times.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_data_init_timeout (default: 120s)
The SMTP client time limit for sending the SMTP DATA command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_data_xfer_timeout (default: 180s)
The SMTP client time limit for sending the SMTP message content. When
the connection makes no progress for more than $smtp_data_xfer_timeout
seconds the Postfix SMTP client terminates the transfer.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_defer_if_no_mx_address_found (default: no)
Defer mail delivery when no MX record resolves to an IP address.

The default (no) is to return the mail as undeliverable. With older
Postfix versions the default was to keep trying to deliver the mail
until someone fixed the MX record or until the mail was too old.

Note: Postfix always ignores MX records with equal or worse preference
than the local MTA itself.

This feature is available in Postfix 2.1 and later.

smtp_destination_concurrency_limit (default: $default_destination_concur-
rency_limit)
The maximal number of parallel deliveries to the same destination via
the smtp message delivery transport. This limit is enforced by the
queue manager. The message delivery transport name is the first field
in the entry in the master.cf file.

smtp_destination_recipient_limit (default: $default_destination_recipi-
ent_limit)
The maximal number of recipients per message for the smtp message
delivery transport. This limit is enforced by the queue manager. The
message delivery transport name is the first field in the entry in the
master.cf file.

Setting this parameter to a value of 1 changes the meaning of smtp_des-
tination_concurrency_limit from concurrency per domain into concurrency
per recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)
Lookup tables, indexed by the remote SMTP server address, with case
insensitive lists of EHLO keywords (pipelining, starttls, auth, etc.)
that the Postfix SMTP client will ignore in the EHLO response from a
remote SMTP server. See smtp_discard_ehlo_keywords for details. The ta-
ble is not indexed by hostname for consistency with smtpd_dis-
card_ehlo_keyword_address_maps.

This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)
A case insensitive list of EHLO keywords (pipelining, starttls, auth,
etc.) that the Postfix SMTP client will ignore in the EHLO response
from a remote SMTP server.

This feature is available in Postfix 2.2 and later.

Notes:

· Specify the silent-discard pseudo keyword to prevent this action
from being logged.

· Use the smtp_discard_ehlo_keyword_address_maps feature to dis-
card EHLO keywords selectively.

smtp_enforce_tls (default: no)
Enforcement mode: require that remote SMTP servers use TLS encryption,
and never send mail in the clear. This also requires that the remote
SMTP server hostname matches the information in the remote server cer-
tificate, and that the remote SMTP server certificate was issued by a
CA that is trusted by the Postfix SMTP client. If the certificate
doesn't verify or the hostname doesn't match, delivery is deferred and
mail stays in the queue.

The server hostname is matched against all names provided as dNSNames
in the SubjectAlternativeName. If no dNSNames are specified, the Com-
monName is checked. The behavior may be changed with the
smtp_tls_enforce_peername option.

This option is useful only if you are definitely sure that you will
only connect to servers that support RFC 2487 _and_ that provide valid
server certificates. Typical use is for clients that send all their
email to a dedicated mailhub.

This feature is available in Postfix 2.2 and later. With Postfix 2.3
and later use smtp_tls_security_level instead.

smtp_fallback_relay (default: $fallback_relay)
Optional list of relay hosts for SMTP destinations that can't be found
or that are unreachable. With Postfix 2.2 and earlier this parameter is
called fallback_relay.

By default, mail is returned to the sender when a destination is not
found, and delivery is deferred when a destination is unreachable.

To prevent mailer loops between MX hosts and fall-back hosts, Postfix
version 2.2 and later will not use the fallback relays for destinations
that it is MX host for (assuming DNS lookup is turned on).

smtp_generic_maps (default: empty)
Optional lookup tables that perform address rewriting in the SMTP
client, typically to transform a locally valid address into a globally
valid address when sending mail across the Internet. This is needed
when the local machine does not have its own Internet domain name, but
uses something like localdomain.local instead.

The table format and lookups are documented in generic(5); examples are
shown in the ADDRESS_REWRITING_README and STANDARD_CONFIGURATION_README
documents.

This feature is available in Postfix 2.2 and later.

smtp_header_checks (default: empty)
Restricted header_checks(5) tables for the Postfix SMTP client. These
tables are searched while mail is being delivered. Actions that change
the delivery time or destination are not available.

This feature is available in Postfix 2.5 and later.

smtp_helo_name (default: $myhostname)
The hostname to send in the SMTP EHLO or HELO command.

The default value is the machine hostname. Specify a hostname or
[ip.add.re.ss].

This information can be specified in the main.cf file for all SMTP
clients, or it can be specified in the master.cf file for a specific
client, for example:

/etc/postfix/master.cf:
mysmtp ... smtp -o smtp_helo_name=foo.bar.com

This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)
The SMTP client time limit for sending the HELO or EHLO command, and
for receiving the initial server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_host_lookup (default: dns)
What mechanisms the Postfix SMTP client uses to look up a host's IP
address. This parameter is ignored when DNS lookups are disabled (see:
disable_dns_lookups).

Specify one of the following:

dns Hosts can be found in the DNS (preferred).

native Use the native naming service only (nsswitch.conf, or equivalent
mechanism).

dns, native
Use the native service for hosts not found in the DNS.

This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 990)
The maximal length of message header and body lines that Postfix will
send via SMTP. Longer lines are broken by inserting "<CR><LF><SPACE>".
This minimizes the damage to MIME formatted mail.

By default, the line length is limited to 990 characters, because some
server implementations cannot receive mail with long lines.

smtp_mail_timeout (default: 300s)
The SMTP client time limit for sending the MAIL FROM command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_mime_header_checks (default: empty)
Restricted mime_header_checks(5) tables for the Postfix SMTP client.
These tables are searched while mail is being delivered. Actions that
change the delivery time or destination are not available.

This feature is available in Postfix 2.5 and later.

smtp_mx_address_limit (default: 5)
The maximal number of MX (mail exchanger) IP addresses that can result
from mail exchanger lookups, or zero (no limit). Prior to Postfix ver-
sion 2.3, this limit was disabled by default.

This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)
The maximal number of SMTP sessions per delivery request before giving
up or delivering to a fall-back relay host, or zero (no limit). This
restriction ignores sessions that fail to complete the SMTP initial
handshake (Postfix version 2.2 and earlier) or that fail to complete
the EHLO and TLS handshake (Postfix version 2.3 and later).

This feature is available in Postfix 2.1 and later.

smtp_nested_header_checks (default: empty)
Restricted nested_header_checks(5) tables for the Postfix SMTP client.
These tables are searched while mail is being delivered. Actions that
change the delivery time or destination are not available.

This feature is available in Postfix 2.5 and later.

smtp_never_send_ehlo (default: no)
Never send EHLO at the start of an SMTP session. See also the
smtp_always_send_ehlo parameter.

smtp_pix_workaround_delay_time (default: 10s)
How long the Postfix SMTP client pauses before sending ".<CR><LF>" in
order to work around the PIX firewall "<CR><LF>.<CR><LF>" bug.

Choosing a too short time makes this workaround ineffective when send-
ing large messages over slow network connections.

smtp_pix_workaround_maps (default: empty)
Lookup tables, indexed by the remote SMTP server address, with per-des-
tination workarounds for CISCO PIX firewall bugs. The table is not
indexed by hostname for consistency with smtp_discard_ehlo_key-
word_address_maps.

This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)
How long a message must be queued before the Postfix SMTP client turns
on the PIX firewall "<CR><LF>.<CR><LF>" bug workaround for delivery
through firewalls with "smtp fixup" mode turned on.

By default, the workaround is turned off for mail that is queued for
less than 500 seconds. In other words, the workaround is normally
turned off for the first delivery attempt.

Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug workaround
upon the first delivery attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
A list that specifies zero or more workarounds for CISCO PIX firewall
bugs. These workarounds are implemented by the Postfix SMTP client.
Workaround names are separated by comma or space, and are case insensi-
tive. This parameter setting can be overruled with per-destination
smtp_pix_workaround_maps settings.

delay_dotcrlf
Insert a delay before sending ".<CR><LF>" after the end of the
message content. The delay is subject to the smtp_pix_work-
around_delay_time and smtp_pix_workaround_threshold_time parame-
ter settings.

disable_esmtp
Disable all extended SMTP commands: send HELO instead of EHLO.

This feature is available in Postfix 2.4 and later. The default set-
tings are backwards compatible with earlier Postfix versions.

smtp_quit_timeout (default: 300s)
The SMTP client time limit for sending the QUIT command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_quote_rfc821_envelope (default: yes)
Quote addresses in SMTP MAIL FROM and RCPT TO commands as required by
RFC 2821. This includes putting quotes around an address localpart that
ends in ".".

The default is to comply with RFC 2821. If you have to send mail to a
broken SMTP server, configure a special SMTP client in master.cf:

/etc/postfix/master.cf:
broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

and route mail for the destination in question to the "broken-smtp"
message delivery with a transport(5) table.

This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)
Randomize the order of equal-preference MX host addresses. This is a
performance feature of the Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)
The SMTP client time limit for sending the SMTP RCPT TO command, and
for receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtp_reply_filter (default: empty)
A mechanism to transform replies from remote SMTP servers one line at a
time. This is a last-resort tool to work around server replies that
break inter-operability with the Postfix SMTP client. Other uses
involve fault injection to test Postfix's handling of invalid
responses.

Notes:

· In the case of a multi-line reply, the Postfix SMTP client uses
the final reply line's numerical SMTP reply code and enhanced
status code.

· The numerical SMTP reply code (XYZ) takes precedence over the
enhanced status code (X.Y.Z). When the enhanced status code
initial digit differs from the SMTP reply code initial digit, or
when no enhanced status code is present, the Postfix SMTP client
uses a generic enhanced status code (X.0.0) instead.

Specify the name of a "type:table" lookup table. The search string is a
single SMTP reply line as received from the remote SMTP server, except
that the trailing <CR><LF> are removed.

Examples:

/etc/postfix/main.cf:
smtp_reply_filter = pcre:/etc/postfix/reply_filter

/etc/postfix/reply_filter:
# Transform garbage into "250-filler..." so that it looks like
# one line from a multi-line reply. It does not matter what we
# substitute here as long it has the right syntax. The Postfix
# SMTP client will use the final line's numerical SMTP reply
# code and enhanced status code.
!/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

This feature is available in Postfix 2.7.

smtp_rset_timeout (default: 20s)
The SMTP client time limit for sending the RSET command, and for
receiving the server response. The SMTP client sends RSET in order to
finish a recipient address probe, or to verify that a cached session is
still usable.

This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_cache_name (default: empty)
An optional table to prevent repeated SASL authentication failures with
the same remote SMTP server hostname, username and password. Each table
(key, value) pair contains a server name, a username and password, and
the full server response. This information is stored when a remote SMTP
server rejects an authentication attempt with a 535 reply code. As
long as the smtp_sasl_password_maps information does no change, and as
long as the smtp_sasl_auth_cache_name information does not expire (see
smtp_sasl_auth_cache_time) the Postfix SMTP client avoids SASL authen-
tication attempts with the same server, username and password, and
instead bounces or defers mail as controlled with the
smtp_sasl_auth_soft_bounce configuration parameter.

Use a per-destination delivery concurrency of 1 (for example,
"smtp_destination_concurrency_limit = 1", "relay_destination_concur-
rency_limit = 1", etc.), otherwise multiple delivery agents may experi-
ence a login failure at the same time.

The table must be accessed via the proxywrite service, i.e. the map
name must start with "proxy:". The table should be stored under the
directory specified with the data_directory parameter.

This feature uses cryptographic hashing to protect plain-text pass-
words, and requires that Postfix is compiled with TLS support.

Example:

smtp_sasl_auth_cache_name = proxy:btree:/var/db/postfix/sasl_auth_cache

This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_cache_time (default: 90d)
The maximal age of an smtp_sasl_auth_cache_name entry before it is
removed.

This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_enable (default: no)
Enable SASL authentication in the Postfix SMTP client. By default, the
Postfix SMTP client uses no authentication.

Example:

smtp_sasl_auth_enable = yes

smtp_sasl_auth_soft_bounce (default: yes)
When a remote SMTP server rejects a SASL authentication request with a
535 reply code, defer mail delivery instead of returning mail as unde-
liverable. The latter behavior was hard-coded prior to Postfix version
2.5.

Note: the setting "yes" overrides the global soft_bounce parameter, but
the setting "no" does not.

Example:

# Default as of Postfix 2.5
smtp_sasl_auth_soft_bounce = yes
# The old hard-coded default
smtp_sasl_auth_soft_bounce = no

This feature is available in Postfix 2.5 and later.

smtp_sasl_mechanism_filter (default: empty)
If non-empty, a Postfix SMTP client filter for the remote SMTP server's
list of offered SASL mechanisms. Different client and server implemen-
tations may support different mechanism lists. By default, the Postfix
SMTP client will use the intersection of the two. smtp_sasl_mecha-
nism_filter further restricts what server mechanisms the client will
take into consideration.

Specify mechanism names, "/file/name" patterns or "type:table" lookup
tables. The right-hand side result from "type:table" lookups is
ignored. Specify "!pattern" to exclude a mechanism name from the list.
The form "!/file/name" is supported only in Postfix version 2.4 and
later.

This feature is available in Postfix 2.2 and later.

Examples:

smtp_sasl_mechanism_filter = plain, login
smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)
Optional SMTP client lookup tables with one username:password entry per
remote hostname or domain, or sender address when sender-dependent
authentication is enabled. If no username:password entry is found,
then the Postfix SMTP client will not attempt to authenticate to the
remote host.

The Postfix SMTP client opens the lookup table before going to chroot
jail, so you can leave the password file in /etc/postfix.

smtp_sasl_path (default: empty)
Implementation-specific information that the Postfix SMTP client passes
through to the SASL plug-in implementation that is selected with
smtp_sasl_type. Typically this specifies the name of a configuration
file or rendezvous point.

This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)
Postfix SMTP client SASL security options; as of Postfix 2.3 the list
of available features depends on the SASL client implementation that is
selected with smtp_sasl_type.

The following security features are defined for the cyrus client SASL
implementation:

Specify zero or more of the following:

noplaintext
Disallow methods that use plaintext passwords.

noactive
Disallow methods subject to active (non-dictionary) attack.

nodictionary
Disallow methods subject to passive (dictionary) attack.

noanonymous
Disallow methods that allow anonymous authentication.

mutual_auth
Only allow methods that provide mutual authentication (not
available with SASL version 1).

Example:

smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
The SASL authentication security options that the Postfix SMTP client
uses for TLS encrypted SMTP sessions.

This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options (default: $smtp_sasl_tls_secu-
rity_options)
The SASL authentication security options that the Postfix SMTP client
uses for TLS encrypted SMTP sessions with a verified server certifi-
cate.

When mail is sent to the public MX host for the recipient's domain,
server certificates are by default optional, and delivery proceeds even
if certificate verification fails. For delivery via a submission ser-
vice that requires SASL authentication, it may be appropriate to send
plaintext passwords only when the connection to the server is strongly
encrypted and the server identity is verified.

The smtp_sasl_tls_verified_security_options parameter makes it possible
to only enable plaintext mechanisms when a secure connection to the
server is available. Submission servers subject to this policy must
either have verifiable certificates or offer suitable non-plaintext
SASL mechanisms.

This feature is available in Postfix 2.6 and later.

smtp_sasl_type (default: cyrus)
The SASL plug-in type that the Postfix SMTP client should use for
authentication. The available types are listed with the "postconf -A"
command.

This feature is available in Postfix 2.3 and later.

smtp_send_xforward_command (default: no)
Send the non-standard XFORWARD command when the Postfix SMTP server
EHLO response announces XFORWARD support.

This allows an "smtp" delivery agent, used for injecting mail into a
content filter, to forward the name, address, protocol and HELO name of
the original client to the content filter and downstream queuing SMTP
server. This can produce more useful logging than localhost[127.0.0.1]
etc.

This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)
Enable sender-dependent authentication in the Postfix SMTP client; this
is available only with SASL authentication, and disables SMTP connec-
tion caching to ensure that mail from different senders will use the
appropriate credentials.

This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)
Skip SMTP servers that greet with a 4XX status code (go away, try again
later).

By default, Postfix moves on the next mail exchanger. Specify
"smtp_skip_4xx_greeting = no" if Postfix should defer delivery immedi-
ately.

This feature is available in Postfix 2.0 and earlier. Later Postfix
versions always skip SMTP servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)
Skip SMTP servers that greet with a 5XX status code (go away, do not
try again later).

By default, the Postfix SMTP client moves on the next mail exchanger.
Specify "smtp_skip_5xx_greeting = no" if Postfix should bounce the mail
immediately. The default setting is incorrect, but it is what a lot of
people expect to happen.

smtp_skip_quit_response (default: yes)
Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)
Time limit for Postfix SMTP client write and read operations during TLS
startup and shutdown handshake procedures.

This feature is available in Postfix 2.2 and later.

smtp_tls_CAfile (default: empty)
A file containing CA certificates of root CAs trusted to sign either
remote SMTP server certificates or intermediate CA certificates. These
are loaded into memory before the smtp(8) client enters the chroot
jail. If the number of trusted roots is large, consider using
smtp_tls_CApath instead, but note that the latter directory must be
present in the chroot jail if the smtp(8) client is chrooted. This file
may also be used to augment the client certificate trust chain, but it
is best to include all the required certificates directly in
$smtp_tls_cert_file.

Specify "tls_append_default_CA = no" to prevent Postfix from appending
the system-supplied default CAs and trusting third-party certificates.

Example:

smtp_tls_CAfile = /etc/postfix/CAcert.pem

This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)
Directory with PEM format certificate authority certificates that the
Postfix SMTP client uses to verify a remote SMTP server certificate.
Don't forget to create the necessary "hash" links with, for example,
"$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

To use this option in chroot mode, this directory (or a copy) must be
inside the chroot jail.

Specify "tls_append_default_CA = no" to prevent Postfix from appending
the system-supplied default CAs and trusting third-party certificates.

Example:

smtp_tls_CApath = /etc/postfix/certs

This feature is available in Postfix 2.2 and later.

smtp_tls_block_early_mail_reply (default: no)
Try to detect a mail hijacking attack based on a TLS protocol vulnera-
bility (CVE-2009-3555), where an attacker prepends malicious HELO,
MAIL, RCPT, DATA commands to a Postfix SMTP client TLS session. The
attack would succeed with non-Postfix SMTP servers that reply to the
malicious HELO, MAIL, RCPT, DATA commands after negotiating the Postfix
SMTP client TLS session.

This feature is available in Postfix 2.7.

smtp_tls_cert_file (default: empty)
File with the Postfix SMTP client RSA certificate in PEM format. This
file may also contain the Postfix SMTP client private RSA key, and
these may be the same as the Postfix SMTP server RSA certificate and
key file.

Do not configure client certificates unless you must present client TLS
certificates to one or more servers. Client certificates are not usu-
ally needed, and can cause problems in configurations that work well
without them. The recommended setting is to let the defaults stand:

smtp_tls_cert_file =
smtp_tls_key_file =
smtp_tls_dcert_file =
smtp_tls_dkey_file =
smtp_tls_eccert_file =
smtp_tls_eckey_file =

The best way to use the default settings is to comment out the above
parameters in main.cf if present.

To enable remote SMTP servers to verify the Postfix SMTP client cer-
tificate, the issuing CA certificates must be made available to the
server. You should include the required certificates in the client cer-
tificate file, the client certificate first, then the issuing CA(s)
(bottom-up order).

Example: the certificate for "client.example.com" was issued by "inter-
mediate CA" which itself has a certificate issued by "root CA". Create
the client.pem file with "cat client_cert.pem intermediate_CA.pem
root_CA.pem > client.pem".

If you also want to verify remote SMTP server certificates issued by
these CAs, you can add the CA certificates to the smtp_tls_CAfile, in
which case it is not necessary to have them in the smtp_tls_cert_file,
smtp_tls_dcert_file or smtp_tls_eccert_file.

A certificate supplied here must be usable as an SSL client certificate
and hence pass the "openssl verify -purpose sslclient ..." test.

Example:

smtp_tls_cert_file = /etc/postfix/client.pem

This feature is available in Postfix 2.2 and later.

smtp_tls_cipherlist (default: empty)
Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS cipher
list. As this feature applies to all TLS security levels, it is easy to
create inter-operability problems by choosing a non-default cipher
list. Do not use a non-default TLS cipher list on hosts that deliver
email to the public Internet: you will be unable to send email to
servers that only support the ciphers you exclude. Using a restricted
cipher list may be more appropriate for an internal MTA, where one can
exert some control over the TLS software and settings of the peer
servers.

Note: do not use "" quotes around the parameter value.

This feature is available in Postfix version 2.2. It is not used with
Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead.

smtp_tls_ciphers (default: export)
The minimum TLS cipher grade that the Postfix SMTP client will use with
opportunistic TLS encryption. Cipher types listed in
smtp_tls_exclude_ciphers are excluded from the base definition of the
selected cipher grade. The default value "export" ensures maximum
inter-operability. Because encryption is optional, stronger controls
are not appropriate, and this setting SHOULD NOT be changed unless the
change is essential.

When TLS is mandatory the cipher grade is chosen via the
smtp_tls_mandatory_ciphers configuration parameter, see there for syn-
tax details. See smtp_tls_policy_maps for information on how to config-
ure ciphers on a per-destination basis.

Example:
smtp_tls_ciphers = export

This feature is available in Postfix 2.6 and later. With earlier Post-
fix releases only the smtp_tls_mandatory_ciphers parameter is imple-
mented, and opportunistic TLS always uses "export" or better (i.e. all)
ciphers.

smtp_tls_dcert_file (default: empty)
File with the Postfix SMTP client DSA certificate in PEM format. This
file may also contain the Postfix SMTP client private DSA key.

See the discussion under smtp_tls_cert_file for more details.

Example:

smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
File with the Postfix SMTP client DSA private key in PEM format. This
file may be combined with the Postfix SMTP client DSA certificate file
specified with $smtp_tls_dcert_file.

The private key must be accessible without a pass-phrase, i.e. it must
not be encrypted. File permissions should grant read-only access to the
system superuser account ("root"), and no access to anyone else.

This feature is available in Postfix 2.2 and later.

smtp_tls_eccert_file (default: empty)
File with the Postfix SMTP client ECDSA certificate in PEM format.
This file may also contain the Postfix SMTP client ECDSA private key.

See the discussion under smtp_tls_cert_file for more details.

Example:

smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_eckey_file (default: $smtp_tls_eccert_file)
File with the Postfix SMTP client ECDSA private key in PEM format.
This file may be combined with the Postfix SMTP client ECDSA certifi-
cate file specified with $smtp_tls_eccert_file.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_enforce_peername (default: yes)
With mandatory TLS encryption, require that the remote SMTP server
hostname matches the information in the remote SMTP server certificate.
As of RFC 2487 the requirements for hostname checking for MTA clients
are not specified.

This option can be set to "no" to disable strict peer name checking.
This setting has no effect on sessions that are controlled via the
smtp_tls_per_site table.

Disabling the hostname verification can make sense in closed environ-
ment where special CAs are created. If not used carefully, this option
opens the danger of a "man-in-the-middle" attack (the CommonName of
this attacker will be logged).

This feature is available in Postfix 2.2 and later. With Postfix 2.3
and later use smtp_tls_security_level instead.

smtp_tls_exclude_ciphers (default: empty)
List of ciphers or cipher types to exclude from the Postfix SMTP client
cipher list at all TLS security levels. This is not an OpenSSL
cipherlist, it is a simple list separated by whitespace and/or commas.
The elements are a single cipher, or one or more "+" separated cipher
properties, in which case only ciphers matching all the properties are
excluded.

Examples (some of these will cause problems):

smtp_tls_exclude_ciphers = aNULL
smtp_tls_exclude_ciphers = MD5, DES
smtp_tls_exclude_ciphers = DES+MD5
smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtp_tls_exclude_ciphers = kEDH+aRSA

The first setting, disables anonymous ciphers. The next setting dis-
ables ciphers that use the MD5 digest algorithm or the (single) DES
encryption algorithm. The next setting disables ciphers that use MD5
and DES together. The next setting disables the two ciphers
"AES256-SHA" and "DES-CBC3-MD5". The last setting disables ciphers that
use "EDH" key exchange with RSA authentication.

This feature is available in Postfix 2.3 and later.

smtp_tls_fingerprint_cert_match (default: empty)
List of acceptable remote SMTP server certificate fingerprints for the
"fingerprint" TLS security level (smtp_tls_security_level = finger-
print). At this security level, certificate authorities are not used,
and certificate expiration times are ignored. Instead, server certifi-
cates are verified directly via their "fingerprint". The fingerprint is
a message digest of the server certificate. The digest algorithm is
selected via the smtp_tls_fingerprint_digest parameter.

When an smtp_tls_policy_maps table entry specifies the "fingerprint"
security level, any "match" attributes in that entry specify the list
of valid fingerprints for the corresponding destination. Multiple fin-
gerprints can be combined with a "|" delimiter in a single match
attribute, or multiple match attributes can be employed.

Example: Certificate fingerprint verification with internal mailhub.
Two matching fingerprints are listed. The relayhost may be multiple
physical hosts behind a load-balancer, each with its own private/public
key and self-signed certificate. Alternatively, a single relayhost may
be in the process of switching from one set of private/public keys to
another, and both keys are trusted just prior to the transition.

relayhost = [mailhub.example.com]
smtp_tls_security_level = fingerprint
smtp_tls_fingerprint_digest = md5
smtp_tls_fingerprint_cert_match =
3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

Example: Certificate fingerprint verification with selected destina-
tions. As in the example above, we show two matching fingerprints:

/etc/postfix/main.cf:
smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
smtp_tls_fingerprint_digest = md5

/etc/postfix/tls_policy:
example.com fingerprint
match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

This feature is available in Postfix 2.5 and later.

smtp_tls_fingerprint_digest (default: md5)
The message digest algorithm used to construct remote SMTP server cer-
tificate fingerprints. At the "fingerprint" TLS security level
(smtp_tls_security_level = fingerprint), the server certificate is ver-
ified by directly matching its fingerprint. The fingerprint is the mes-
sage digest of the server certificate using the selected algorithm.
With a digest algorithm resistant to "second pre-image" attacks, it is
not feasible to create a new public key and a matching certificate that
has the same fingerprint.

The default algorithm is md5; this is consistent with the backwards
compatible setting of the digest used to verify client certificates in
the SMTP server.

The best practice algorithm is now sha1. Recent advances in hash func-
tion cryptanalysis have led to md5 being deprecated in favor of sha1.
However, as long as there are no known "second pre-image" attacks
against md5, its use in this context can still be considered safe.

While additional digest algorithms are often available with OpenSSL's
libcrypto, only those used by libssl in SSL cipher suites are available
to Postfix. For now this means just md5 or sha1.

To find the fingerprint of a specific certificate file, with a specific
digest algorithm, run:

$ openssl x509 -noout -fingerprint -digest -in certfile.pem

The text to the right of "=" sign is the desired fingerprint. For
example:

$ openssl x509 -noout -fingerprint -sha1 -in cert.pem
SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

This feature is available in Postfix 2.5 and later.

smtp_tls_key_file (default: $smtp_tls_cert_file)
File with the Postfix SMTP client RSA private key in PEM format. This
file may be combined with the Postfix SMTP client RSA certificate file
specified with $smtp_tls_cert_file.

Example:

smtp_tls_key_file = $smtp_tls_cert_file

This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)
Enable additional Postfix SMTP client logging of TLS activity. Each
logging level also includes the information that is logged at a lower
logging level.

0 Disable logging of TLS activity.

1 Log TLS handshake and certificate information.

2 Log levels during TLS negotiation.

3 Log hexadecimal and ASCII dump of TLS negotiation process.

4 Log hexadecimal and ASCII dump of complete transmission after
STARTTLS.

Use "smtp_tls_loglevel = 3" only in case of problems. Use of loglevel 4
is strongly discouraged.

This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)
The minimum TLS cipher grade that the Postfix SMTP client will use with
mandatory TLS encryption. The default value "medium" is suitable for
most destinations with which you may want to enforce TLS, and is beyond
the reach of today's cryptanalytic methods. See smtp_tls_policy_maps
for information on how to configure ciphers on a per-destination basis.

The following cipher grades are supported:

export Enable "EXPORT" grade or better OpenSSL ciphers. This is the
default for opportunistic encryption. It is not recommended for
mandatory encryption unless you must enforce TLS with "crippled"
peers. The underlying cipherlist is specified via the
tls_export_cipherlist configuration parameter, which you are
strongly encouraged to not change.

low Enable "LOW" grade or better OpenSSL ciphers. This setting is
only appropriate for internal mail servers. The underlying
cipherlist is specified via the tls_low_cipherlist configuration
parameter, which you are strongly encouraged to not change.

medium Enable "MEDIUM" grade or better OpenSSL ciphers. The underlying
cipherlist is specified via the tls_medium_cipherlist configura-
tion parameter, which you are strongly encouraged to not change.

high Enable only "HIGH" grade OpenSSL ciphers. This setting may be
appropriate when all mandatory TLS destinations (e.g. when all
mail is routed to a suitably capable relayhost) support at least
one "HIGH" grade cipher. The underlying cipherlist is specified
via the tls_high_cipherlist configuration parameter, which you
are strongly encouraged to not change.

null Enable only the "NULL" OpenSSL ciphers, these provide authenti-
cation without encryption. This setting is only appropriate in
the rare case that all servers are prepared to use NULL ciphers
(not normally enabled in TLS servers). A plausible use-case is
an LMTP server listening on a UNIX-domain socket that is config-
ured to support "NULL" ciphers. The underlying cipherlist is
specified via the tls_null_cipherlist configuration parameter,
which you are strongly encouraged to not change.

The underlying cipherlists for grades other than "null" include anony-
mous ciphers, but these are automatically filtered out if the Postfix
SMTP client is configured to verify server certificates. You are very
unlikely to need to take any steps to exclude anonymous ciphers, they
are excluded automatically as necessary. If you must exclude anonymous
ciphers at the "may" or "encrypt" security levels, when the Postfix
SMTP client does not need or use peer certificates, set
"smtp_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only
when TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)
Additional list of ciphers or cipher types to exclude from the SMTP
client cipher list at mandatory TLS security levels. This list works in
addition to the exclusions listed with smtp_tls_exclude_ciphers (see
there for syntax details).

Starting with Postfix 2.6, the mandatory cipher exclusions can be spec-
ified on a per-destination basis via the TLS policy "exclude"
attribute. See smtp_tls_policy_maps for notes and examples.

This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: SSLv3, TLSv1)
List of SSL/TLS protocols that the Postfix SMTP client will use with
mandatory TLS encryption. In main.cf the values are separated by
whitespace, commas or colons. In the policy table "protocols" attribute
(see smtp_tls_policy_maps) the only valid separator is colon. An empty
value means allow all protocols. The valid protocol names, (see \fBfBSSL_get_version(3)
), are "SSLv2", "SSLv3" and "TLSv1".

With Postfix >= 2.5 the parameter syntax is expanded to support proto-
col exclusions. One can now explicitly exclude SSLv2 by setting
"smtp_tls_mandatory_protocols = !SSLv2". To exclude both SSLv2 and
SSLv3 set "smtp_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing the
protocols to include, rather than protocols to exclude, is still sup-
ported; use the form you find more intuitive.

Since SSL version 2 has known protocol weaknesses and is now depre-
cated, the default setting excludes "SSLv2". This means that by
default, SSL version 2 will not be used at the "encrypt" security level
and higher.

See the documentation of the smtp_tls_policy_maps parameter and
TLS_README for more information about security levels.

Example:

smtp_tls_mandatory_protocols = TLSv1
# Alternative form with Postfix >= 2.5:
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3

This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)
Log the hostname of a remote SMTP server that offers STARTTLS, when TLS
is not already enabled for that server.

The logfile record looks like:

postfix/smtp[pid]: Host offered STARTTLS: [name.of.host]

This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)
Optional lookup tables with the Postfix SMTP client TLS usage policy by
next-hop destination and by remote SMTP server hostname. When both
lookups succeed, the more specific per-site policy (NONE, MUST, etc)
overrides the less specific one (MAY), and the more secure per-site
policy (MUST, etc) overrides the less secure one (NONE). With Postfix
2.3 and later smtp_tls_per_site is strongly discouraged: use
smtp_tls_policy_maps instead.

Use of the bare hostname as the per-site table lookup key is discour-
aged. Always use the full destination nexthop (enclosed in [] with a
possible ":port" suffix). A recipient domain or MX-enabled transport
next-hop with no port suffix may look like a bare hostname, but is
still a suitable destination.

Specify a next-hop destination or server hostname on the left-hand
side; no wildcards are allowed. The next-hop destination is either the
recipient domain, or the destination specified with a transport(5) ta-
ble, the relayhost parameter, or the relay_transport parameter. On the
right hand side specify one of the following keywords:

NONE Don't use TLS at all. This overrides a less specific MAY lookup
result from the alternate host or next-hop lookup key, and over-
rides the global smtp_use_tls, smtp_enforce_tls, and
smtp_tls_enforce_peername settings.

MAY Try to use TLS if the server announces support, otherwise use
the unencrypted connection. This has less precedence than a more
specific result (including NONE) from the alternate host or
next-hop lookup key, and has less precedence than the more spe-
cific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peer-
name = yes".

MUST_NOPEERMATCH
Require TLS encryption, but do not require that the remote SMTP
server hostname matches the information in the remote SMTP
server certificate, or that the server certificate was issued by
a trusted CA. This overrides a less secure NONE or a less spe-
cific MAY lookup result from the alternate host or next-hop
lookup key, and overrides the global smtp_use_tls,
smtp_enforce_tls and smtp_tls_enforce_peername settings.

MUST Require TLS encryption, require that the remote SMTP server
hostname matches the information in the remote SMTP server cer-
tificate, and require that the remote SMTP server certificate
was issued by a trusted CA. This overrides a less secure NONE
and MUST_NOPEERMATCH or a less specific MAY lookup result from
the alternate host or next-hop lookup key, and overrides the
global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peer-
name settings.

The above keywords correspond to the "none", "may", "encrypt" and "ver-
ify" security levels for the new smtp_tls_security_level parameter
introduced in Postfix 2.3. Starting with Postfix 2.3, and independently
of how the policy is specified, the smtp_tls_mandatory_ciphers and
smtp_tls_mandatory_protocols parameters apply when TLS encryption is
mandatory. Connections for which encryption is optional typically
enable all "export" grade and better ciphers (see smtp_tls_ciphers and
smtp_tls_protocols).

As long as no secure DNS lookup mechanism is available, false hostnames
in MX or CNAME responses can change the server hostname that Postfix
uses for TLS policy lookup and server certificate verification. Even
with a perfect match between the server hostname and the server cer-
tificate, there is no guarantee that Postfix is connected to the right
server. See TLS_README (Closing a DNS loophole with obsolete per-site
TLS policies) for a possible work-around.

This feature is available in Postfix 2.2 and later. With Postfix 2.3
and later use smtp_tls_policy_maps instead.

smtp_tls_policy_maps (default: empty)
Optional lookup tables with the Postfix SMTP client TLS security policy
by next-hop destination; when a non-empty value is specified, this
overrides the obsolete smtp_tls_per_site parameter. See TLS_README for
a more detailed discussion of TLS security levels.

The TLS policy table is indexed by the full next-hop destination, which
is either the recipient domain, or the verbatim next-hop specified in
the transport table, $local_transport, $virtual_transport,
$relay_transport or $default_transport. This includes any enclosing
square brackets and any non-default destination server port suffix. The
LMTP socket type prefix (inet: or unix:) is not included in the lookup
key.

Only the next-hop domain, or $myhostname with LMTP over UNIX-domain
sockets, is used as the nexthop name for certificate verification. The
port and any enclosing square brackets are used in the table lookup
key, but are not used for server name verification.

When the lookup key is a domain name without enclosing square brackets
or any :port suffix (typically the recipient domain), and the full
domain is not found in the table, just as with the transport(5) table,
the parent domain starting with a leading "." is matched recursively.
This allows one to specify a security policy for a recipient domain and
all its sub-domains.

The lookup result is a security level, followed by an optional list of
whitespace and/or comma separated name=value attributes that override
related main.cf settings. The TLS security levels in order of increas-
ing security are:

none No TLS. No additional attributes are supported at this level.

may Opportunistic TLS. Since sending in the clear is acceptable,
demanding stronger than default TLS security merely reduces
inter-operability. The optional "ciphers", "exclude" and "proto-
cols" attributes (available for opportunistic TLS with Postfix
>= 2.6) override the "smtp_tls_ciphers",
"smtp_tls_exclude_ciphers" and "smtp_tls_protocols" configura-
tion parameters. When opportunistic TLS handshakes fail, Postfix
retries the connection with TLS disabled. This allows mail
delivery to sites with non-interoperable TLS implementations.

encrypt
Mandatory TLS encryption. At this level and higher, the optional
"protocols" attribute overrides the main.cf smtp_tls_manda-
tory_protocols parameter, the optional "ciphers" attribute over-
rides the main.cf smtp_tls_mandatory_ciphers parameter, and the
optional "exclude" attribute (Postfix >= 2.6) overrides the
main.cf smtp_tls_mandatory_exclude_ciphers parameter. In the
policy table, multiple protocols or excluded ciphers must be
separated by colons, as attribute values may not contain white-
space or commas.

fingerprint
Certificate fingerprint verification. Available with Postfix 2.5
and later. At this security level, there are no trusted certifi-
cate authorities. The certificate trust chain, expiration date,
... are not checked. Instead, the optional match attribute, or
else the main.cf smtp_tls_fingerprint_cert_match parameter,
lists the valid "fingerprints" of the server certificate. The
digest algorithm used to calculate the fingerprint is selected
by the smtp_tls_fingerprint_digest parameter. Multiple finger-
prints can be combined with a "|" delimiter in a single match
attribute, or multiple match attributes can be employed. The ":"
character is not used as a delimiter as it occurs between each
pair of fingerprint (hexadecimal) digits.

verify Mandatory TLS verification. At this security level, DNS MX
lookups are trusted to be secure enough, and the name verified
in the server certificate is usually obtained indirectly via
unauthenticated DNS MX lookups. The optional "match" attribute
overrides the main.cf smtp_tls_verify_cert_match parameter. In
the policy table, multiple match patterns and strategies must be
separated by colons. In practice explicit control over matching
is more common with the "secure" policy, described below.

secure Secure-channel TLS. At this security level, DNS MX lookups,
though potentially used to determine the candidate next-hop
gateway IP addresses, are not trusted to be secure enough for
TLS peername verification. Instead, the default name verified in
the server certificate is obtained directly from the next-hop,
or is explicitly specified via the optional match attribute
which overrides the main.cf smtp_tls_secure_cert_match parame-
ter. In the policy table, multiple match patterns and strategies
must be separated by colons. The match attribute is most useful
when multiple domains are supported by common server, the policy
entries for additional domains specify matching rules for the
primary domain certificate. While transport table overrides
routing the secondary domains to the primary nexthop also allow
secure verification, they risk delivery to the wrong destination
when domains change hands or are re-assigned to new gateways.
With the "match" attribute approach, routing is not perturbed,
and mail is deferred if verification of a new MX host fails.

Example:

/etc/postfix/main.cf:
smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
# Postfix 2.5 and later
smtp_tls_fingerprint_digest = md5

/etc/postfix/tls_policy:
example.edu none
example.mil may
example.gov encrypt protocols=TLSv1
example.com verify ciphers=high
example.net secure
.example.net secure match=.example.net:example.net
[mail.example.org]:587 secure match=nexthop
# Postfix 2.5 and later
[thumb.example.org] fingerprint
match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

Note: The hostname strategy if listed in a non-default setting of
smtp_tls_secure_cert_match or in the match attribute in the policy ta-
ble can render the secure level vulnerable to DNS forgery. Do not use
the hostname strategy for secure-channel configurations in environments
where DNS security is not assured.

This feature is available in Postfix 2.3 and later.

smtp_tls_protocols (default: !SSLv2)
List of TLS protocols that the Postfix SMTP client will exclude or
include with opportunistic TLS encryption. Starting with Postfix 2.6,
the Postfix SMTP client will by default not use the obsolete SSLv2 pro-
tocol.

In main.cf the values are separated by whitespace, commas or colons. In
the policy table (see smtp_tls_policy_maps) the only valid separator is
colon. An empty value means allow all protocols. The valid protocol
names, (see \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

To include a protocol list its name, to exclude it, prefix the name
with a "!" character. To exclude SSLv2 even for opportunistic TLS set
"smtp_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
"smtp_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the protocols
to include, is supported, but not recommended. OpenSSL provides no
mechanisms for excluding protocols not known at compile-time. If Post-
fix is linked against an OpenSSL library that supports additional pro-
tocol versions, they cannot be excluded using either syntax.

Example:
# TLSv1 only!
smtp_tls_protocols = !SSLv2, !SSLv3

This feature is available in Postfix 2.6 and later.

smtp_tls_scert_verifydepth (default: 9)
The verification depth for remote SMTP server certificates. A depth of
1 is sufficient if the issuing CA is listed in a local CA file.

The default verification depth is 9 (the OpenSSL default) for compati-
bility with earlier Postfix behavior. Prior to Postfix 2.5, the default
value was 5, but the limit was not actually enforced. If you have set
this to a lower non-default value, certificates with longer trust
chains may now fail to verify. Certificate chains with 1 or 2 CAs are
common, deeper chains are more rare and any number between 5 and 9
should suffice in practice. You can choose a lower number if, for exam-
ple, you trust certificates directly signed by an issuing CA but not
any CAs it delegates to.

This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)
The server certificate peername verification method for the "secure"
TLS security level. In a "secure" TLS policy table ($smtp_tls_pol-
icy_maps) entry the optional "match" attribute overrides this main.cf
setting.

This parameter specifies one or more patterns or strategies separated
by commas, whitespace or colons. In the policy table the only valid
separator is the colon character.

For a description of the pattern and strategy syntax see the
smtp_tls_verify_cert_match parameter. The "hostname" strategy should be
avoided in this context, as in the absence of a secure global DNS,
using the results of MX lookups in certificate verification is not
immune to active (man-in-the-middle) attacks on DNS.

Sample main.cf setting:

smtp_tls_secure_cert_match = nexthop

Sample policy table override:

example.net secure match=example.com:.example.com
.example.net secure match=example.com:.example.com

This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)
The default SMTP TLS security level for the Postfix SMTP client; when a
non-empty value is specified, this overrides the obsolete parameters
smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername.

Specify one of the following security levels:

none TLS will not be used unless enabled for specific destinations
via smtp_tls_policy_maps.

may Opportunistic TLS. Use TLS if this is supported by the remote
SMTP server, otherwise use plaintext. Since sending in the clear
is acceptable, demanding stronger than default TLS security
merely reduces inter-operability. The "smtp_tls_ciphers" and
"smtp_tls_protocols" (Postfix >= 2.6) configuration parameters
provide control over the protocols and cipher grade used with
opportunistic TLS. With earlier releases the opportunistic TLS
cipher grade is always "export" and no protocols are disabled.
When TLS handshakes fail, the connection is retried with TLS
disabled. This allows mail delivery to sites with non-interop-
erable TLS implementations.

encrypt
Mandatory TLS encryption. Since a minimum level of security is
intended, it is reasonable to be specific about sufficiently
secure protocol versions and ciphers. At this security level and
higher, the main.cf parameters smtp_tls_mandatory_protocols and
smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
cipher grade which the administrator considers secure enough for
mandatory encrypted sessions. This security level is not an
appropriate default for systems delivering mail to the Internet.

verify Mandatory TLS verification. At this security level, DNS MX
lookups are trusted to be secure enough, and the name verified
in the server certificate is usually obtained indirectly via
unauthenticated DNS MX lookups. The smtp_tls_verify_cert_match
parameter controls how the server name is verified. In practice
explicit control over matching is more common at the "secure"
level, described below. This security level is not an appropri-
ate default for systems delivering mail to the Internet.

Examples:

# No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
smtp_tls_security_level = none

# Opportunistic TLS.
smtp_tls_security_level = may
# Postfix >= 2.6:
# Do not tweak opportunistic ciphers or protocol unless it is essential
# to do so (if a security vulnerability is found in the SSL library that
# can be mitigated by disabling a particular protocol or raising the
# cipher grade from "export" to "low" or "medium").
smtp_tls_ciphers = export
smtp_tls_protocols = !SSLv2

# Mandatory (high-grade) TLS encryption.
smtp_tls_security_level = encrypt
smtp_tls_mandatory_ciphers = high

# Mandatory TLS verification of hostname or nexthop domain.
smtp_tls_security_level = verify
smtp_tls_mandatory_ciphers = high
smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

# Secure channel TLS with exact nexthop name match.
smtp_tls_security_level = secure
smtp_tls_mandatory_protocols = TLSv1
smtp_tls_mandatory_ciphers = high
smtp_tls_secure_cert_match = nexthop

# Certificate fingerprint verification (Postfix >= 2.5).
# The CA-less "fingerprint" security level only scales to a limited
# number of destinations. As a global default rather than a per-site
# setting, this is practical when mail for all recipients is sent
# to a central mail hub.
relayhost = [mailhub.example.com]
smtp_tls_security_level = fingerprint
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
smtp_tls_mandatory_ciphers = high
smtp_tls_fingerprint_cert_match =
3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

This feature is available in Postfix 2.3 and later.

smtp_tls_session_cache_database (default: empty)
Name of the file containing the optional Postfix SMTP client TLS ses-
sion cache. Specify a database type that supports enumeration, such as
btree or sdbm; there is no need to support concurrent access. The file
is created if it does not exist. The smtp(8) daemon does not use this
parameter directly, rather the cache is implemented indirectly in the
tlsmgr(8) daemon. This means that per-smtp-instance master.cf overrides
of this parameter are not effective. Note, that each of the cache
databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data-
base, $smtp_tls_session_cache_database (and with Postfix 2.3 and later
$lmtp_tls_session_cache_database), needs to be stored separately. It is
not at this time possible to store multiple caches in a single data-
base.

Note: dbm databases are not suitable. TLS session objects are too
large.

As of version 2.5, Postfix no longer uses root privileges when opening
this file. The file should now be stored under the Postfix-owned
data_directory. As a migration aid, an attempt to open the file under a
non-Postfix directory is redirected to the Postfix-owned data_direc-
tory, and a warning is logged.

Example:

smtp_tls_session_cache_database = btree:/var/db/postfix/smtp_scache

This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)
The expiration time of Postfix SMTP client TLS session cache informa-
tion. A cache cleanup is performed periodically every $smtp_tls_ses-
sion_cache_timeout seconds. As with $smtp_tls_session_cache_database,
this parameter is implemented in the tlsmgr(8) daemon and therefore
per-smtp-instance master.cf overrides are not possible.

This feature is available in Postfix 2.2 and later.

smtp_tls_verify_cert_match (default: hostname)
The server certificate peername verification method for the "verify"
TLS security level. In a "verify" TLS policy table ($smtp_tls_pol-
icy_maps) entry the optional "match" attribute overrides this main.cf
setting.

This parameter specifies one or more patterns or strategies separated
by commas, whitespace or colons. In the policy table the only valid
separator is the colon character.

Patterns specify domain names, or domain name suffixes:

example.com
Match the example.com domain, i.e. one of the names the server
certificate must be example.com, upper and lower case distinc-
tions are ignored.

.example.com
Match subdomains of the example.com domain, i.e. match a name in
the server certificate that consists of a non-zero number of
labels followed by a .example.com suffix. Case distinctions are
ignored.

Strategies specify a transformation from the next-hop domain to the
expected name in the server certificate:

nexthop
Match against the next-hop domain, which is either the recipient
domain, or the transport next-hop configured for the domain
stripped of any optional socket type prefix, enclosing square
brackets and trailing port. When MX lookups are not suppressed,
this is the original nexthop domain prior to the MX lookup, not
the result of the MX lookup. For LMTP delivery via UNIX-domain
sockets, the verified next-hop name is $myhostname. This strat-
egy is suitable for use with the "secure" policy. Case is
ignored.

dot-nexthop
As above, but match server certificate names that are subdomains
of the next-hop domain. Case is ignored.

hostname
Match against the hostname of the server, often obtained via an
unauthenticated DNS MX lookup. For LMTP delivery via UNIX-domain
sockets, the verified name is $myhostname. This matches the ver-
ification strategy of the "MUST" keyword in the obsolete
smtp_tls_per_site table, and is suitable for use with the "ver-
ify" security level. When the next-hop name is enclosed in
square brackets to suppress MX lookups, the "hostname" strategy
is the same as the "nexthop" strategy. Case is ignored.

Sample main.cf setting:

smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

Sample policy table override:

example.com verify match=hostname:nexthop
.example.com verify match=example.com:.example.com:hostname

This feature is available in Postfix 2.3 and later.

smtp_use_tls (default: no)
Opportunistic mode: use TLS when a remote SMTP server announces START-
TLS support, otherwise send the mail in the clear. Beware: some SMTP
servers offer STARTTLS even if it is not configured. With Postfix <
2.3, if the TLS handshake fails, and no other server is available,
delivery is deferred and mail stays in the queue. If this is a concern
for you, use the smtp_tls_per_site feature instead.

This feature is available in Postfix 2.2 and later. With Postfix 2.3
and later use smtp_tls_security_level instead.

smtp_xforward_timeout (default: 300s)
The SMTP client time limit for sending the XFORWARD command, and for
receiving the server response.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)
What SMTP clients are allowed to specify the XVERP command. This com-
mand requests that mail be delivered one recipient at a time with a per
recipient return address.

By default, no clients are allowed to specify XVERP.

This parameter was renamed with Postfix version 2.1. The default value
is backwards compatible with Postfix version 2.0.

Note: IP version 6 address information must be specified inside [] in
the smtpd_authorized_verp_clients value, and in files specified with
"/file/name". IP version 6 addresses contain the ":" character, and
would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xclient_hosts (default: empty)
What SMTP clients are allowed to use the XCLIENT feature. This command
overrides SMTP client information that is used for access control. Typ-
ical use is for SMTP-based content filters, fetchmail-like programs, or
SMTP server access rule testing. See the XCLIENT_README document for
details.

This feature is available in Postfix 2.1 and later.

By default, no clients are allowed to specify XCLIENT.

Note: IP version 6 address information must be specified inside [] in
the smtpd_authorized_xclient_hosts value, and in files specified with
"/file/name". IP version 6 addresses contain the ":" character, and
would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xforward_hosts (default: empty)
What SMTP clients are allowed to use the XFORWARD feature. This com-
mand forwards information that is used to improve logging after SMTP-
based content filters. See the XFORWARD_README document for details.

This feature is available in Postfix 2.1 and later.

By default, no clients are allowed to specify XFORWARD.

Note: IP version 6 address information must be specified inside [] in
the smtpd_authorized_xforward_hosts value, and in files specified with
"/file/name". IP version 6 addresses contain the ":" character, and
would otherwise be confused with a "type:table" pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)
The text that follows the 220 status code in the SMTP greeting banner.
Some people like to see the mail version advertised. By default, Post-
fix shows no version.

You MUST specify $myhostname at the start of the text. This is required
by the SMTP protocol.

Example:

smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_connection_count_limit (default: 50)
How many simultaneous connections any client is allowed to make to this
service. By default, the limit is set to half the default process
limit value.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be
used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)
The maximal number of connection attempts any client is allowed to make
to this service per time unit. The time unit is specified with the
anvil_rate_time_unit configuration parameter.

By default, a client can make as many connections per time unit as
Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be
used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)
Clients that are excluded from connection count, connection rate, or
SMTP request rate restrictions. See the mynetworks parameter descrip-
tion for the parameter value syntax.

By default, clients in trusted networks are excluded. Specify a list of
network blocks, hostnames or .domain names (the initial dot causes the
domain to match any name below it).

Note: IP version 6 address information must be specified inside [] in
the smtpd_client_event_limit_exceptions value, and in files specified
with "/file/name". IP version 6 addresses contain the ":" character,
and would otherwise be confused with a "type:table" pattern.

This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)
The maximal number of message delivery requests that any client is
allowed to make to this service per time unit, regardless of whether or
not Postfix actually accepts those messages. The time unit is speci-
fied with the anvil_rate_time_unit configuration parameter.

By default, a client can send as many message delivery requests per
time unit as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be
used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)
The maximal number of new (i.e., uncached) TLS sessions that a remote
SMTP client is allowed to negotiate with this service per time unit.
The time unit is specified with the anvil_rate_time_unit configuration
parameter.

By default, a remote SMTP client can negotiate as many new TLS sessions
per time unit as Postfix can accept.

To disable this feature, specify a limit of 0. Otherwise, specify a
limit that is at least the per-client concurrent session limit, or else
legitimate client sessions may be rejected.

WARNING: The purpose of this feature is to limit abuse. It must not be
used to regulate legitimate mail traffic.

This feature is available in Postfix 2.3 and later.

Example:

smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_port_logging (default: no)
Enable logging of the remote SMTP client port in addition to the host-
name and IP address. The logging format is "host[address]:port".

This feature is available in Postfix 2.5 and later.

smtpd_client_recipient_rate_limit (default: 0)
The maximal number of recipient addresses that any client is allowed to
send to this service per time unit, regardless of whether or not Post-
fix actually accepts those recipients. The time unit is specified with
the anvil_rate_time_unit configuration parameter.

By default, a client can send as many recipient addresses per time unit
as Postfix can accept.

To disable this feature, specify a limit of 0.

WARNING: The purpose of this feature is to limit abuse. It must not be
used to regulate legitimate mail traffic.

This feature is available in Postfix 2.2 and later.

Example:

smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)
Optional SMTP server access restrictions in the context of a client
SMTP connection request. See SMTPD_ACCESS_README, section "Delayed
evaluation of SMTP access restriction lists" for a discussion of evalu-
ation context and time.

The default is to allow all connection requests.

Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
Restrictions are applied in the order as specified; the first restric-
tion that matches wins.

The following restrictions are specific to client hostname or client
network address information.

check_ccert_access type:table
Use the client certificate fingerprint as lookup key for the
specified access(5) database; with Postfix version 2.2, also
require that the SMTP client certificate is verified success-
fully. The fingerprint digest algorithm is configurable via the
smtpd_tls_fingerprint_digest parameter (hard-coded as md5 prior
to Postfix version 2.5). This feature is available with Postfix
version 2.2 and later.

check_client_access type:table
Search the specified access database for the client hostname,
parent domains, client IP address, or networks obtained by
stripping least significant octets. See the access(5) manual
page for details.

check_client_mx_access type:table
Search the specified access(5) database for the MX hosts for the
client hostname, and execute the corresponding action. Note: a
result of "OK" is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from blacklists. This
feature is available in Postfix 2.7 and later.

check_client_ns_access type:table
Search the specified access(5) database for the DNS servers for
the client hostname, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from
blacklists. This feature is available in Postfix 2.7 and later.

check_reverse_client_hostname_access type:table
Search the specified access database for the unverified reverse
client hostname, parent domains, client IP address, or networks
obtained by stripping least significant octets. See the
access(5) manual page for details. Note: a result of "OK" is
not allowed for safety reasons. Instead, use DUNNO in order to
exclude specific hosts from blacklists. This feature is avail-
able in Postfix 2.6 and later.

check_reverse_client_hostname_mx_access type:table
Search the specified access(5) database for the MX hosts for the
unverified reverse client hostname, and execute the correspond-
ing action. Note: a result of "OK" is not allowed for safety
reasons. Instead, use DUNNO in order to exclude specific hosts
from blacklists. This feature is available in Postfix 2.7 and
later.

check_reverse_client_hostname_ns_access type:table
Search the specified access(5) database for the DNS servers for
the unverified reverse client hostname, and execute the corre-
sponding action. Note: a result of "OK" is not allowed for
safety reasons. Instead, use DUNNO in order to exclude specific
hosts from blacklists. This feature is available in Postfix 2.7
and later.

permit_inet_interfaces
Permit the request when the client IP address matches
$inet_interfaces.

permit_mynetworks
Permit the request when the client IP address matches any net-
work or network address listed in $mynetworks.

permit_sasl_authenticated
Permit the request when the client is successfully authenticated
via the RFC 4954 (AUTH) protocol.

permit_tls_all_clientcerts
Permit the request when the remote SMTP client certificate is
verified successfully. This option must be used only if a spe-
cial CA issues the certificates and only this CA is listed as
trusted CA. Otherwise, clients with a third-party certificate
would also be allowed to relay. Specify "tls_append_default_CA
= no" when the trusted CA is specified with smtpd_tls_CAfile or
smtpd_tls_CApath, to prevent Postfix from appending the system-
supplied default CAs. This feature is available with Postfix
version 2.2.

permit_tls_clientcerts
Permit the request when the remote SMTP client certificate fin-
gerprint is listed in $relay_clientcerts. The fingerprint
digest algorithm is configurable via the smtpd_tls_finger-
print_digest parameter (hard-coded as md5 prior to Postfix ver-
sion 2.5). This feature is available with Postfix version 2.2.

reject_rbl_client rbl_domain=d.d.d.d
Reject the request when the reversed client network address is
listed with the A record "d.d.d.d" under rbl_domain (Postfix
version 2.1 and later only). If no "=d.d.d.d" is specified,
reject the request when the reversed client network address is
listed with any A record under rbl_domain.
The maps_rbl_reject_code parameter specifies the response code
for rejected requests (default: 554), the default_rbl_reply
parameter specifies the default server reply, and the
rbl_reply_maps parameter specifies tables with server replies
indexed by rbl_domain. This feature is available in Postfix 2.0
and later.

reject_rhsbl_client rbl_domain=d.d.d.d
Reject the request when the client hostname is listed with the A
record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
only). If no "=d.d.d.d" is specified, reject the request when
the client hostname is listed with any A record under
rbl_domain. See the reject_rbl_client description above for
additional RBL related configuration parameters. This feature
is available in Postfix 2.0 and later.

reject_unknown_client_hostname (with Postfix < 2.3:
reject_unknown_client)
Reject the request when 1) the client IP address->name mapping
fails, 2) the name->address mapping fails, or 3) the
name->address mapping does not match the client IP address.
This is a stronger restriction than the
reject_unknown_reverse_client_hostname feature, which triggers
only under condition 1) above.
The unknown_client_reject_code parameter specifies the response
code for rejected requests (default: 450). The reply is always
450 in case the address->name or name->address lookup failed due
to a temporary problem.

reject_unknown_reverse_client_hostname
Reject the request when the client IP address has no
address->name mapping.
This is a weaker restriction than the
reject_unknown_client_hostname feature, which requires not only
that the address->name and name->address mappings exist, but
also that the two mappings reproduce the client IP address.
The unknown_client_reject_code parameter specifies the response
code for rejected requests (default: 450). The reply is always
450 in case the address->name lookup failed due to a temporary
problem.
This feature is available in Postfix 2.3 and later.

In addition, you can use any of the following generic restrictions.
These restrictions are applicable in any SMTP command context.

check_policy_service servername
Query the specified policy server. See the SMTPD_POLICY_README
document for details. This feature is available in Postfix 2.1
and later.

defer Defer the request. The client is told to try again later. This
restriction is useful at the end of a restriction list, to make
the default policy explicit.
The defer_code parameter specifies the SMTP server reply code
(default: 450).

defer_if_permit
Defer the request if some later restriction would result in an
explicit or implicit PERMIT action. This is useful when a
blacklisting feature fails due to a temporary problem. This
feature is available in Postfix version 2.1 and later.

defer_if_reject
Defer the request if some later restriction would result in a
REJECT action. This is useful when a whitelisting feature fails
due to a temporary problem. This feature is available in Post-
fix version 2.1 and later.

permit Permit the request. This restriction is useful at the end of a
restriction list, to make the default policy explicit.

reject_multi_recipient_bounce
Reject the request when the envelope sender is the null address,
and the message has multiple envelope recipients. This usage has
rare but legitimate applications: under certain conditions,
multi-recipient mail that was posted with the DSN option
NOTIFY=NEVER may be forwarded with the null sender address.
Note: this restriction can only work reliably when used in
smtpd_data_restrictions or smtpd_end_of_data_restrictions,
because the total number of recipients is not known at an ear-
lier stage of the SMTP conversation. Use at the RCPT stage will
only reject the second etc. recipient.
The multi_recipient_bounce_reject_code parameter specifies the
response code for rejected requests (default: 550). This fea-
ture is available in Postfix 2.1 and later.

reject_plaintext_session
Reject the request when the connection is not encrypted. This
restriction should not be used before the client has had a
chance to negotiate encryption with the AUTH or STARTTLS com-
mands.
The plaintext_reject_code parameter specifies the response code
for rejected requests (default: 450). This feature is avail-
able in Postfix 2.3 and later.

reject_unauth_pipelining
Reject the request when the client sends SMTP commands ahead of
time where it is not allowed, or when the client sends SMTP com-
mands ahead of time without knowing that Postfix actually sup-
ports ESMTP command pipelining. This stops mail from bulk mail
software that improperly uses ESMTP command pipelining in order
to speed up deliveries.
With Postfix 2.6 and later, the SMTP server sets a per-session
flag whenever it detects illegal pipelining, including pipelined
EHLO or HELO commands. The reject_unauth_pipelining feature sim-
ply tests whether the flag was set at any point in time during
the session.
With older Postfix versions, reject_unauth_pipelining checks the
current status of the input read queue, and its usage is not
recommended in contexts other than smtpd_data_restrictions.

reject Reject the request. This restriction is useful at the end of a
restriction list, to make the default policy explicit. The
reject_code configuration parameter specifies the response code
for rejected requests (default: 554).

sleep seconds
Pause for the specified number of seconds and proceed with the
next restriction in the list, if any. This may stop zombie mail
when used as:
/etc/postfix/main.cf:
smtpd_client_restrictions =
sleep 1, reject_unauth_pipelining
smtpd_delay_reject = no
This feature is available in Postfix 2.3.

warn_if_reject
Change the meaning of the next restriction, so that it logs a
warning instead of rejecting a request (look for logfile records
that contain "reject_warning"). This is useful for testing new
restrictions in a "live" environment without risking unnecessary
loss of mail.

Other restrictions that are valid in this context:

· SMTP command specific restrictions that are described under the
smtpd_helo_restrictions, smtpd_sender_restrictions or
smtpd_recipient_restrictions parameters. When helo, sender or
recipient restrictions are listed under smtpd_client_restric-
tions, they have effect only with "smtpd_delay_reject = yes", so
that $smtpd_client_restrictions is evaluated at the time of the
RCPT TO command.

Example:

smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_command_filter (default: empty)
A mechanism to transform commands from remote SMTP clients. This is a
last-resort tool to work around client commands that break inter-oper-
ability with the Postfix SMTP server. Other uses involve fault injec-
tion to test Postfix's handling of invalid commands.

Specify the name of a "type:table" lookup table. The search string is
the SMTP command as received from the remote SMTP client, except that
initial whitespace and the trailing <CR><LF> are removed. The result
value is executed by the Postfix SMTP server.

Postfix already implements a number of workarounds for malformed client
commands.

· Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

· Postfix already accepts the correct form "user@[ipaddress]".

· Use "strict_rfc821_envelopes = no" to accept "User Name
<user@example.com>". Postfix will ignore the "User Name" part
before delivering the mail.

Examples:

/etc/postfix/main.cf:
smtpd_command_filter = pcre:/etc/postfix/command_filter

/etc/postfix/command_filter:
# Work around clients that send malformed HELO commands.
/^HELO\s*$/ HELO domain.invalid

# Work around clients that send empty lines.
/^\s*$/ NOOP

# Work around clients that send RCPT TO:<'user@domain'>.
# WARNING: do not lose the parameters that follow the address.
/^RCPT\s+TO:\s*<'([^[:space:]]+)'>(.*)/ RCPT TO:<$1>$2

This feature is available in Postfix 2.7.

smtpd_data_restrictions (default: empty)
Optional access restrictions that the Postfix SMTP server applies in
the context of the SMTP DATA command. See SMTPD_ACCESS_README, section
"Delayed evaluation of SMTP access restriction lists" for a discussion
of evaluation context and time.

This feature is available in Postfix 2.0 and later.

The following restrictions are valid in this context:

· Generic restrictions that can be used in any SMTP command con-
text, described under smtpd_client_restrictions.

· SMTP command specific restrictions described under
smtpd_client_restrictions, smtpd_helo_restrictions,
smtpd_sender_restrictions or smtpd_recipient_restrictions.

Examples:

smtpd_data_restrictions = reject_unauth_pipelining
smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)
Postpone the start of an SMTP mail transaction until a valid RCPT TO
command is received. Specify "no" to create a mail transaction as soon
as the SMTP server receives a valid MAIL FROM command.

With sites that reject lots of mail, the default setting reduces the
use of disk, CPU and memory resources. The downside is that rejected
recipients are logged with NOQUEUE instead of a mail transaction ID.
This complicates the logfile analysis of multi-recipient mail.

This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)
Wait until the RCPT TO command before evaluating $smtpd_client_restric-
tions, $smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait
until the ETRN command before evaluating $smtpd_client_restrictions and
$smtpd_helo_restrictions.

This feature is turned on by default because some clients apparently
mis-behave when the Postfix SMTP server rejects commands before RCPT
TO.

The default setting has one major benefit: it allows Postfix to log
recipient address information when rejecting a client name/address or
sender address, so that it is possible to find out whose mail is being
rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)
Lookup tables, indexed by the remote SMTP client address, with case
insensitive lists of EHLO keywords (pipelining, starttls, auth, etc.)
that the SMTP server will not send in the EHLO response to a remote
SMTP client. See smtpd_discard_ehlo_keywords for details. The table is
not searched by hostname for robustness reasons.

This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
A case insensitive list of EHLO keywords (pipelining, starttls, auth,
etc.) that the SMTP server will not send in the EHLO response to a
remote SMTP client.

This feature is available in Postfix 2.2 and later.

Notes:

· Specify the silent-discard pseudo keyword to prevent this action
from being logged.

· Use the smtpd_discard_ehlo_keyword_address_maps feature to dis-
card EHLO keywords selectively.

smtpd_end_of_data_restrictions (default: empty)
Optional access restrictions that the Postfix SMTP server applies in
the context of the SMTP END-OF-DATA command. See SMTPD_ACCESS_README,
section "Delayed evaluation of SMTP access restriction lists" for a
discussion of evaluation context and time.

This feature is available in Postfix 2.2 and later.

See smtpd_data_restrictions for syntax details.

smtpd_enforce_tls (default: no)
Mandatory TLS: announce STARTTLS support to SMTP clients, and require
that clients use TLS encryption. According to RFC 2487 this MUST NOT
be applied in case of a publicly-referenced SMTP server. This option
is off by default and should be used only on dedicated servers.

Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".

Note 2: when invoked via "sendmail -bs", Postfix will never offer
STARTTLS due to insufficient privileges to access the server private
key. This is intended behavior.

This feature is available in Postfix 2.2 and later. With Postfix 2.3
and later use smtpd_tls_security_level instead.

smtpd_error_sleep_time (default: 1s)
With Postfix version 2.1 and later: the SMTP server response delay
after a client has made more than $smtpd_soft_error_limit errors, and
fewer than $smtpd_hard_error_limit errors, without delivering mail.

With Postfix version 2.0 and earlier: the SMTP server delay before
sending a reject (4xx or 5xx) response, when the client has made fewer
than $smtpd_soft_error_limit errors without delivering mail.

smtpd_etrn_restrictions (default: empty)
Optional SMTP server access restrictions in the context of a client
ETRN request. See SMTPD_ACCESS_README, section "Delayed evaluation of
SMTP access restriction lists" for a discussion of evaluation context
and time.

The Postfix ETRN implementation accepts only destinations that are eli-
gible for the Postfix "fast flush" service. See the ETRN_README file
for details.

The following restrictions are specific to the domain name information
received with the ETRN command.

check_etrn_access type:table
Search the specified access database for the ETRN domain name or
its parent domains. See the access(5) manual page for details.

Other restrictions that are valid in this context:

· Generic restrictions that can be used in any SMTP command con-
text, described under smtpd_client_restrictions.

· SMTP command specific restrictions described under
smtpd_client_restrictions and smtpd_helo_restrictions.

Example:

smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)
What characters are allowed in $name expansions of RBL reply templates.
Characters not in the allowed set are replaced by "_". Use C like
escapes to specify special characters such as whitespace.

This parameter is not subjected to $parameter expansion.

This feature is available in Postfix 2.0 and later.

smtpd_forbidden_commands (default: CONNECT, GET, POST)
List of commands that causes the Postfix SMTP server to immediately
terminate the session with a 221 code. This can be used to disconnect
clients that obviously attempt to abuse the system. In addition to the
commands listed in this parameter, commands that follow the "Label:"
format of message headers will also cause a disconnect.

This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: normal: 20, stress: 1)
The maximal number of errors a remote SMTP client is allowed to make
without delivering mail. The Postfix SMTP server disconnects when the
limit is exceeded. Normally the default limit is 20, but it changes
under overload to just 1 with Postfix 2.6 and later.

smtpd_helo_required (default: no)
Require that a remote SMTP client introduces itself with the HELO or
EHLO command before sending the MAIL command or other commands that
require EHLO negotiation.

Example:

smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
Optional restrictions that the Postfix SMTP server applies in the con-
text of the SMTP HELO command. See SMTPD_ACCESS_README, section
"Delayed evaluation of SMTP access restriction lists" for a discussion
of evaluation context and time.

The default is to permit everything.

The following restrictions are specific to the hostname information
received with the HELO or EHLO command.

check_helo_access type:table
Search the specified access(5) database for the HELO or EHLO
hostname or parent domains, and execute the corresponding
action.

check_helo_mx_access type:table
Search the specified access(5) database for the MX hosts for the
HELO or EHLO hostname, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from
blacklists. This feature is available in Postfix 2.1 and later.

check_helo_ns_access type:table
Search the specified access(5) database for the DNS servers for
the HELO or EHLO hostname, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from
blacklists. This feature is available in Postfix 2.1 and later.

reject_invalid_helo_hostname (with Postfix < 2.3: reject_invalid_host-
name)
Reject the request when the HELO or EHLO hostname syntax is
invalid.
The invalid_hostname_reject_code specifies the response code for
rejected requests (default: 501).

reject_non_fqdn_helo_hostname (with Postfix < 2.3:
reject_non_fqdn_hostname)
Reject the request when the HELO or EHLO hostname is not in
fully-qualified domain form, as required by the RFC.
The non_fqdn_reject_code parameter specifies the response code
for rejected requests (default: 504).

reject_rhsbl_helo rbl_domain=d.d.d.d
Reject the request when the HELO or EHLO hostname hostname is
listed with the A record "d.d.d.d" under rbl_domain (Postfix
version 2.1 and later only). If no "=d.d.d.d" is specified,
reject the request when the HELO or EHLO hostname is listed with
any A record under rbl_domain. See the reject_rbl_client
description for additional RBL related configuration parameters.
This feature is available in Postfix 2.0 and later.

reject_unknown_helo_hostname (with Postfix < 2.3: reject_unknown_host-
name)
Reject the request when the HELO or EHLO hostname has no DNS A
or MX record.
The unknown_hostname_reject_code parameter specifies the numeri-
cal response code for rejected requests (default: 450).
The unknown_helo_hostname_tempfail_action parameter specifies
the action after a temporary DNS error (default: defer_if_per-
mit).

Other restrictions that are valid in this context:

· Generic restrictions that can be used in any SMTP command con-
text, described under smtpd_client_restrictions.

· Client hostname or network address specific restrictions
described under smtpd_client_restrictions.

· SMTP command specific restrictions described under
smtpd_sender_restrictions or smtpd_recipient_restrictions. When
sender or recipient restrictions are listed under
smtpd_helo_restrictions, they have effect only with
"smtpd_delay_reject = yes", so that $smtpd_helo_restrictions is
evaluated at the time of the RCPT TO command.

Examples:

smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)
The maximal number of lines in the Postfix SMTP server command history
before it is flushed upon receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: normal: 100, stress: 1)
The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote
SMTP client can send before the Postfix SMTP server starts to increment
the error counter with each junk command. The junk command count is
reset after mail is delivered. See also the smtpd_error_sleep_time and
smtpd_soft_error_limit configuration parameters. Normally the default
limit is 100, but it changes under overload to just 1 with Postfix 2.6
and later.

smtpd_milters (default: empty)
A list of Milter (mail filter) applications for new mail that arrives
via the Postfix smtpd(8) server. See the MILTER_README document for
details.

This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)
List of commands that the Postfix SMTP server replies to with "250 Ok",
without doing any syntax checks and without changing state. This list
overrides any commands built into the Postfix SMTP server.

smtpd_null_access_lookup_key (default: <>)
The lookup key to be used in SMTP access(5) tables instead of the null
sender address.

smtpd_peername_lookup (default: yes)
Attempt to look up the remote SMTP client hostname, and verify that the
name matches the client IP address. A client name is set to "unknown"
when it cannot be looked up or verified, or when name lookup is dis-
abled. Turning off name lookup reduces delays due to DNS lookup and
increases the maximal inbound delivery rate.

This feature is available in Postfix 2.3 and later.

smtpd_policy_service_max_idle (default: 300s)
The time after which an idle SMTPD policy service connection is closed.

This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)
The time after which an active SMTPD policy service connection is
closed.

This feature is available in Postfix 2.1 and later.

smtpd_policy_service_timeout (default: 100s)
The time limit for connecting to, writing to or receiving from a dele-
gated SMTPD policy server.

This feature is available in Postfix 2.1 and later.

smtpd_proxy_ehlo (default: $myhostname)
How the Postfix SMTP server announces itself to the proxy filter. By
default, the Postfix hostname is used.

This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)
The hostname and TCP port of the mail filtering proxy server. The
proxy receives all mail from the Postfix SMTP server, and is supposed
to give the result to another Postfix SMTP server process.

Specify "host:port" or "inet:host:port" for a TCP endpoint, or
"unix:pathname" for a UNIX-domain endpoint. The host can be specified
as an IP address or as a symbolic name; no MX lookups are done. When
no "host" or "host:" are specified, the local machine is assumed.
Pathname interpretation is relative to the Postfix queue directory.

This feature is available in Postfix 2.1 and later.

The "inet:" and "unix:" prefixes are available in Postfix 2.3 and
later.

smtpd_proxy_options (default: empty)
List of options that control how the Postfix SMTP server communicates
with a before-queue content filter. Specify zero or more of the follow-
ing, separated by comma or whitespace.

speed_adjust
Do not connect to a before-queue content filter until an entire
message has been received. This reduces the number of simultane-
ous before-queue content filter processes.

NOTE 1: A filter must not selectively reject recipients of a multi-
recipient message. Rejecting all recipients is OK, as is accepting all
recipients.

NOTE 2: This feature increases the minimum amount of free queue space
by $message_size_limit. The extra space is needed to save the message
to a temporary file.

This feature is available in Postfix 2.7 and later.

smtpd_proxy_timeout (default: 100s)
The time limit for connecting to a proxy filter and for sending or
receiving information. When a connection fails the client gets a
generic error message while more detailed information is logged to the
maillog file.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)
The maximal number of recipients that the Postfix SMTP server accepts
per message delivery request.

smtpd_recipient_overshoot_limit (default: 1000)
The number of recipients that a remote SMTP client can send in excess
of the limit specified with $smtpd_recipient_limit, before the Postfix
SMTP server increments the per-session error count for each excess
recipient.

smtpd_recipient_restrictions (default: permit_mynetworks, reject_unauth_desti-
nation)
The access restrictions that the Postfix SMTP server applies in the
context of the RCPT TO command. See SMTPD_ACCESS_README, section
"Delayed evaluation of SMTP access restriction lists" for a discussion
of evaluation context and time.

By default, the Postfix SMTP server accepts:

· Mail from clients whose IP address matches $mynetworks, or:

· Mail to remote destinations that match $relay_domains, except
for addresses that contain sender-specified routing (user@else-
where@domain), or:

· Mail to local destinations that match $inet_interfaces or
$proxy_interfaces, $mydestination, $virtual_alias_domains, or
$virtual_mailbox_domains.

IMPORTANT: If you change this parameter setting, you must specify at
least one of the following restrictions. Otherwise Postfix will refuse
to receive mail:

reject, defer, defer_if_permit, reject_unauth_destination

The following restrictions are specific to the recipient address that
is received with the RCPT TO command.

check_recipient_access type:table
Search the specified access(5) database for the resolved RCPT TO
address, domain, parent domains, or localpart@, and execute the
corresponding action.

check_recipient_mx_access type:table
Search the specified access(5) database for the MX hosts for the
RCPT TO domain, and execute the corresponding action. Note: a
result of "OK" is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from blacklists. This
feature is available in Postfix 2.1 and later.

check_recipient_ns_access type:table
Search the specified access(5) database for the DNS servers for
the RCPT TO domain, and execute the corresponding action. Note:
a result of "OK" is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from blacklists. This
feature is available in Postfix 2.1 and later.

permit_auth_destination
Permit the request when one of the following is true:

· Postfix is mail forwarder: the resolved RCPT TO domain matches
$relay_domains or a subdomain thereof, and the address contains
no sender-specified routing (user@elsewhere@domain),

· Postfix is the final destination: the resolved RCPT TO domain
matches $mydestination, $inet_interfaces, $proxy_interfaces,
$virtual_alias_domains, or $virtual_mailbox_domains, and the
address contains no sender-specified routing (user@else-
where@domain).

permit_mx_backup
Permit the request when the local mail system is backup MX for
the RCPT TO domain, or when the domain is an authorized destina-
tion (see permit_auth_destination for definition).

· Safety: permit_mx_backup does not accept addresses that have
sender-specified routing information (example: user@else-
where@domain).

· Safety: permit_mx_backup can be vulnerable to mis-use when
access is not restricted with permit_mx_backup_networks.

· Safety: as of Postfix version 2.3, permit_mx_backup no longer
accepts the address when the local mail system is primary MX for
the recipient domain. Exception: permit_mx_backup accepts the
address when it specifies an authorized destination (see per-
mit_auth_destination for definition).

· Limitation: mail may be rejected in case of a temporary DNS
lookup problem with Postfix prior to version 2.0.

reject_non_fqdn_recipient
Reject the request when the RCPT TO address is not in fully-
qualified domain form, as required by the RFC.
The non_fqdn_reject_code parameter specifies the response code
for rejected requests (default: 504).

reject_rhsbl_recipient rbl_domain=d.d.d.d
Reject the request when the RCPT TO domain is listed with the A
record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
only). If no "=d.d.d.d" is specified, reject the request when
the RCPT TO domain is listed with any A record under rbl_domain.
The maps_rbl_reject_code parameter specifies the response code
for rejected requests (default: 554); the default_rbl_reply
parameter specifies the default server reply; and the
rbl_reply_maps parameter specifies tables with server replies
indexed by rbl_domain. This feature is available in Postfix
version 2.0 and later.

reject_unauth_destination
Reject the request unless one of the following is true:

· Postfix is mail forwarder: the resolved RCPT TO domain matches
$relay_domains or a subdomain thereof, and contains no sender-
specified routing (user@elsewhere@domain),

· Postfix is the final destination: the resolved RCPT TO domain
matches $mydestination, $inet_interfaces, $proxy_interfaces,
$virtual_alias_domains, or $virtual_mailbox_domains, and con-
tains no sender-specified routing (user@elsewhere@domain).
The relay_domains_reject_code parameter specifies the response
code for rejected requests (default: 554).

reject_unknown_recipient_domain
Reject the request when Postfix is not final destination for the
recipient domain, and the RCPT TO domain has no DNS A or MX
record, or when it has a malformed MX record such as a record
with a zero-length MX hostname (Postfix version 2.3 and later).
The unknown_address_reject_code parameter specifies the numeri-
cal response code for rejected requests (default: 450). The
response is always 450 in case of a temporary DNS error.
The unknown_address_tempfail_action parameter specifies the
action after a temporary DNS error (default: defer_if_permit).

reject_unlisted_recipient (with Postfix version 2.0: check_recipi-
ent_maps)
Reject the request when the RCPT TO address is not listed in the
list of valid recipients for its domain class. See the
smtpd_reject_unlisted_recipient parameter description for
details. This feature is available in Postfix 2.1 and later.

reject_unverified_recipient
Reject the request when mail to the RCPT TO address is known to
bounce, or when the recipient address destination is not reach-
able. Address verification information is managed by the ver-
ify(8) server; see the ADDRESS_VERIFICATION_README file for
details.
The unverified_recipient_reject_code parameter specifies the
numerical response code when an address is known to bounce
(default: 450, change into 550 when you are confident that it is
safe to do so).
The unverified_recipient_defer_code parameter specifies the
numerical response code when an address probe failed due to a
temporary problem (default: 450).
The unverified_recipient_tempfail_action parameter specifies the
action after addres probe failure due to a temporary problem
(default: defer_if_permit).
This feature is available in Postfix 2.1 and later.

Other restrictions that are valid in this context:

· Generic restrictions that can be used in any SMTP command con-
text, described under smtpd_client_restrictions.

· SMTP command specific restrictions described under
smtpd_client_restrictions, smtpd_helo_restrictions and
smtpd_sender_restrictions.

Example:

smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_unlisted_recipient (default: yes)
Request that the Postfix SMTP server rejects mail for unknown recipient
addresses, even when no explicit reject_unlisted_recipient access
restriction is specified. This prevents the Postfix queue from filling
up with undeliverable MAILER-DAEMON messages.

An address is always considered "known" when it matches a virtual(5)
alias or a canonical(5) mapping.

· The recipient domain matches $mydestination, $inet_interfaces or
$proxy_interfaces, but the recipient is not listed in
$local_recipient_maps, and $local_recipient_maps is not null.

· The recipient domain matches $virtual_alias_domains but the
recipient is not listed in $virtual_alias_maps.

· The recipient domain matches $virtual_mailbox_domains but the
recipient is not listed in $virtual_mailbox_maps, and $vir-
tual_mailbox_maps is not null.

· The recipient domain matches $relay_domains but the recipient is
not listed in $relay_recipient_maps, and $relay_recipient_maps
is not null.

This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)
Request that the Postfix SMTP server rejects mail from unknown sender
addresses, even when no explicit reject_unlisted_sender access restric-
tion is specified. This can slow down an explosion of forged mail from
worms or viruses.

An address is always considered "known" when it matches a virtual(5)
alias or a canonical(5) mapping.

· The sender domain matches $mydestination, $inet_interfaces or
$proxy_interfaces, but the sender is not listed in $local_recip-
ient_maps, and $local_recipient_maps is not null.

· The sender domain matches $virtual_alias_domains but the sender
is not listed in $virtual_alias_maps.

· The sender domain matches $virtual_mailbox_domains but the
sender is not listed in $virtual_mailbox_maps, and $vir-
tual_mailbox_maps is not null.

· The sender domain matches $relay_domains but the sender is not
listed in $relay_recipient_maps, and $relay_recipient_maps is
not null.

This feature is available in Postfix 2.1 and later.

smtpd_restriction_classes (default: empty)
User-defined aliases for groups of access restrictions. The aliases can
be specified in smtpd_recipient_restrictions etc., and on the right-
hand side of a Postfix access(5) table.

One major application is for implementing per-recipient UCE control.
See the RESTRICTION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)
The application name that the Postfix SMTP server uses for SASL server
initialization. This controls the name of the SASL configuration file.
The default value is smtpd, corresponding to a SASL configuration file
named smtpd.conf.

This feature is available in Postfix 2.1 and 2.2. With Postfix 2.3 it
was renamed to smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)
Enable SASL authentication in the Postfix SMTP server. By default, the
Postfix SMTP server does not use authentication.

If a remote SMTP client is authenticated, the permit_sasl_authenticated
access restriction can be used to permit relay access, like this:

smtpd_recipient_restrictions =
permit_mynetworks, permit_sasl_authenticated, ...

To reject all SMTP connections from unauthenticated clients, specify
"smtpd_delay_reject = yes" (which is the default) and use:

smtpd_client_restrictions = permit_sasl_authenticated, reject

See the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)
Report the SASL authenticated user name in the smtpd(8) Received mes-
sage header.

This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)
What remote SMTP clients the Postfix SMTP server will not offer AUTH
support to.

Some clients (Netscape 4 at least) have a bug that causes them to
require a login and password whenever AUTH is offered, whether it's
necessary or not. To work around this, specify, for example, $mynet-
works to prevent Postfix from offering AUTH to local clients.

Specify a list of network/netmask patterns, separated by commas and/or
whitespace. The mask specifies the number of bits in the network part
of a host address. You can also "/file/name" or "type:table" patterns.
A "/file/name" pattern is replaced by its contents; a "type:table"
lookup table is matched when a table entry matches a lookup string (the
lookup result is ignored). Continue long lines by starting the next
line with whitespace. Specify "!pattern" to exclude an address or net-
work block from the list. The form "!/file/name" is supported only in
Postfix version 2.4 and later.

Note: IP version 6 address information must be specified inside [] in
the smtpd_sasl_exceptions_networks value, and in files specified with
"/file/name". IP version 6 addresses contain the ":" character, and
would otherwise be confused with a "type:table" pattern.

Example:

smtpd_sasl_exceptions_networks = $mynetworks

This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)
The name of the Postfix SMTP server's local SASL authentication realm.

By default, the local authentication realm name is the null string.

Examples:

smtpd_sasl_local_domain = $mydomain
smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)
Implementation-specific information that the Postfix SMTP server passes
through to the SASL plug-in implementation that is selected with
smtpd_sasl_type. Typically this specifies the name of a configuration
file or rendezvous point.

This feature is available in Postfix 2.3 and later. In earlier releases
it was called smtpd_sasl_application_name.

smtpd_sasl_security_options (default: noanonymous)
Postfix SMTP server SASL security options; as of Postfix 2.3 the list
of available features depends on the SASL server implementation that is
selected with smtpd_sasl_type.

The following security features are defined for the cyrus server SASL
implementation:

Restrict what authentication mechanisms the Postfix SMTP server will
offer to the client. The list of available authentication mechanisms
is system dependent.

Specify zero or more of the following:

noplaintext
Disallow methods that use plaintext passwords.

noactive
Disallow methods subject to active (non-dictionary) attack.

nodictionary
Disallow methods subject to passive (dictionary) attack.

noanonymous
Disallow methods that allow anonymous authentication.

forward_secrecy
Only allow methods that support forward secrecy (Dovecot only).

mutual_auth
Only allow methods that provide mutual authentication (not
available with Cyrus SASL version 1).

By default, the Postfix SMTP server accepts plaintext passwords but not
anonymous logins.

Warning: it appears that clients try authentication methods in the
order as advertised by the server (e.g., PLAIN ANONYMOUS CRAM-MD5)
which means that if you disable plaintext passwords, clients will log
in anonymously, even when they should be able to use CRAM-MD5. So, if
you disable plaintext logins, disable anonymous logins too. Postfix
treats anonymous login as no authentication.

Example:

smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
The SASL authentication security options that the Postfix SMTP server
uses for TLS encrypted SMTP sessions.

This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)
The SASL plug-in type that the Postfix SMTP server should use for
authentication. The available types are listed with the "postconf -a"
command.

This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)
Optional lookup table with the SASL login names that own sender (MAIL
FROM) addresses.

Specify zero or more "type:table" lookup tables. With lookups from
indexed files such as DB or DBM, or from networked tables such as NIS,
LDAP or SQL, the following search operations are done with a sender
address of user@domain:

1) user@domain
This table lookup is always done and has the highest precedence.

2) user
This table lookup is done only when the domain part of the
sender address matches $myorigin, $mydestination, $inet_inter-
faces or $proxy_interfaces.

3) @domain
This table lookup is done last and has the lowest precedence.

In all cases the result of table lookup must be either "not found" or a
list of SASL login names separated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)
Optional restrictions that the Postfix SMTP server applies in the con-
text of the MAIL FROM command. See SMTPD_ACCESS_README, section
"Delayed evaluation of SMTP access restriction lists" for a discussion
of evaluation context and time.

The default is to permit everything.

The following restrictions are specific to the sender address received
with the MAIL FROM command.

check_sender_access type:table
Search the specified access(5) database for the MAIL FROM
address, domain, parent domains, or localpart@, and execute the
corresponding action.

check_sender_mx_access type:table
Search the specified access(5) database for the MX hosts for the
MAIL FROM address, and execute the corresponding action. Note:
a result of "OK" is not allowed for safety reasons. Instead, use
DUNNO in order to exclude specific hosts from blacklists. This
feature is available in Postfix 2.1 and later.

check_sender_ns_access type:table
Search the specified access(5) database for the DNS servers for
the MAIL FROM address, and execute the corresponding action.
Note: a result of "OK" is not allowed for safety reasons.
Instead, use DUNNO in order to exclude specific hosts from
blacklists. This feature is available in Postfix 2.1 and later.

reject_authenticated_sender_login_mismatch
Enforces the reject_sender_login_mismatch restriction for
authenticated clients only. This feature is available in Postfix
version 2.1 and later.

reject_non_fqdn_sender
Reject the request when the MAIL FROM address is not in fully-
qualified domain form, as required by the RFC.
The non_fqdn_reject_code parameter specifies the response code
for rejected requests (default: 504).

reject_rhsbl_sender rbl_domain=d.d.d.d
Reject the request when the MAIL FROM domain is listed with the
A record "d.d.d.d" under rbl_domain (Postfix version 2.1 and
later only). If no "=d.d.d.d" is specified, reject the request
when the MAIL FROM domain is listed with any A record under
rbl_domain.
The maps_rbl_reject_code parameter specifies the response code
for rejected requests (default: 554); the default_rbl_reply
parameter specifies the default server reply; and the
rbl_reply_maps parameter specifies tables with server replies
indexed by rbl_domain. This feature is available in Postfix 2.0
and later.

reject_sender_login_mismatch
Reject the request when $smtpd_sender_login_maps specifies an
owner for the MAIL FROM address, but the client is not (SASL)
logged in as that MAIL FROM address owner; or when the client is
(SASL) logged in, but the client login name doesn't own the MAIL
FROM address according to $smtpd_sender_login_maps.

reject_unauthenticated_sender_login_mismatch
Enforces the reject_sender_login_mismatch restriction for unau-
thenticated clients only. This feature is available in Postfix
version 2.1 and later.

reject_unknown_sender_domain
Reject the request when Postfix is not final destination for the
sender address, and the MAIL FROM address has no DNS A or MX
record, or when it has a malformed MX record such as a record
with a zero-length MX hostname (Postfix version 2.3 and later).
The unknown_address_reject_code parameter specifies the numeri-
cal response code for rejected requests (default: 450). The
response is always 450 in case of a temporary DNS error.
The unknown_address_tempfail_action parameter specifies the
action after a temporary DNS error (default: defer_if_permit).

reject_unlisted_sender
Reject the request when the MAIL FROM address is not listed in
the list of valid recipients for its domain class. See the
smtpd_reject_unlisted_sender parameter description for details.
This feature is available in Postfix 2.1 and later.

reject_unverified_sender
Reject the request when mail to the MAIL FROM address is known
to bounce, or when the sender address destination is not reach-
able. Address verification information is managed by the ver-
ify(8) server; see the ADDRESS_VERIFICATION_README file for
details.
The unverified_sender_reject_code parameter specifies the numer-
ical response code when an address is known to bounce (default:
450, change into 550 when you are confident that it is safe to
do so).
The unverified_sender_defer_code specifies the numerical
response code when an address address probe failed due to a tem-
porary problem (default: 450).
The unverified_sender_tempfail_action parameter specifies the
action after address probe failure due to a temporary problem
(default: defer_if_permit).
This feature is available in Postfix 2.1 and later.

Other restrictions that are valid in this context:

· Generic restrictions that can be used in any SMTP command con-
text, described under smtpd_client_restrictions.

· SMTP command specific restrictions described under
smtpd_client_restrictions and smtpd_helo_restrictions.

· SMTP command specific restrictions described under smtpd_recipi-
ent_restrictions. When recipient restrictions are listed under
smtpd_sender_restrictions, they have effect only with
"smtpd_delay_reject = yes", so that $smtpd_sender_restrictions
is evaluated at the time of the RCPT TO command.

Examples:

smtpd_sender_restrictions = reject_unknown_sender_domain
smtpd_sender_restrictions = reject_unknown_sender_domain,
check_sender_access hash:/etc/postfix/access

smtpd_soft_error_limit (default: 10)
The number of errors a remote SMTP client is allowed to make without
delivering mail before the Postfix SMTP server slows down all its
responses.

· With Postfix version 2.1 and later, the Postfix SMTP server
delays all responses by $smtpd_error_sleep_time seconds.

· With Postfix versions 2.0 and earlier, the Postfix SMTP server
delays all responses by (number of errors) seconds.

smtpd_starttls_timeout (default: 300s)
The time limit for Postfix SMTP server write and read operations during
TLS startup and shutdown handshake procedures.

This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, stress: 10s)
The time limit for sending a Postfix SMTP server response and for
receiving a remote SMTP client request. Normally the default limit is
300s, but it changes under overload to just 10s with Postfix 2.6 and
later.

Note: if you set SMTP time limits to very large values you may have to
update the global ipc_timeout parameter.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

smtpd_tls_CAfile (default: empty)
A file containing (PEM format) CA certificates of root CAs trusted to
sign either remote SMTP client certificates or intermediate CA certifi-
cates. These are loaded into memory before the smtpd(8) server enters
the chroot jail. If the number of trusted roots is large, consider
using smtpd_tls_CApath instead, but note that the latter directory must
be present in the chroot jail if the smtpd(8) server is chrooted. This
file may also be used to augment the server certificate trust chain,
but it is best to include all the required certificates directly in the
server certificate file.

Specify "tls_append_default_CA = no" to prevent Postfix from appending
the system-supplied default CAs and trusting third-party certificates.

By default (see smtpd_tls_ask_ccert), client certificates are not
requested, and smtpd_tls_CAfile should remain empty. If you do make use
of client certificates, the distinguished names (DNs) of the certifi-
cate authorities listed in smtpd_tls_CAfile are sent to the remote SMTP
client in the client certificate request message. MUAs with multiple
client certificates may use the list of preferred certificate authori-
ties to select the correct client certificate. You may want to put
your "preferred" CA or CAs in this file, and install other trusted CAs
in $smtpd_tls_CApath.

Example:

smtpd_tls_CAfile = /etc/postfix/CAcert.pem

This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
A directory containing (PEM format) CA certificates of root CAs trusted
to sign either remote SMTP client certificates or intermediate CA cer-
tificates. Do not forget to create the necessary "hash" links with, for
example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs". To use
smtpd_tls_CApath in chroot mode, this directory (or a copy) must be
inside the chroot jail.

Specify "tls_append_default_CA = no" to prevent Postfix from appending
the system-supplied default CAs and trusting third-party certificates.

By default (see smtpd_tls_ask_ccert), client certificates are not
requested, and smtpd_tls_CApath should remain empty. In contrast to
smtpd_tls_CAfile, DNs of certificate authorities installed in
$smtpd_tls_CApath are not included in the client certificate request
message. MUAs with multiple client certificates may use the list of
preferred certificate authorities to select the correct client certifi-
cate. You may want to put your "preferred" CA or CAs in
$smtpd_tls_CAfile, and install the remaining trusted CAs in
$smtpd_tls_CApath.

Example:

smtpd_tls_CApath = /etc/postfix/certs

This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)
Force the Postfix SMTP server to issue a TLS session id, even when TLS
session caching is turned off (smtpd_tls_session_cache_database is
empty). This behavior is compatible with Postfix < 2.3.

With Postfix 2.3 and later the Postfix SMTP server can disable session
id generation when TLS session caching is turned off. This keeps
clients from caching sessions that almost certainly cannot be re-used.

By default, the Postfix SMTP server always generates TLS session ids.
This works around a known defect in mail client applications such as MS
Outlook, and may also prevent interoperability issues with other MTAs.

Example:

smtpd_tls_always_issue_session_ids = no

This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)
Ask a remote SMTP client for a client certificate. This information is
needed for certificate based mail relaying with, for example, the per-
mit_tls_clientcerts feature.

Some clients such as Netscape will either complain if no certificate is
available (for the list of CAs in $smtpd_tls_CAfile) or will offer mul-
tiple client certificates to choose from. This may be annoying, so this
option is "off" by default.

This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)
When TLS encryption is optional in the Postfix SMTP server, do not
announce or accept SASL authentication over unencrypted connections.

This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 9)
The verification depth for remote SMTP client certificates. A depth of
1 is sufficient if the issuing CA is listed in a local CA file.

This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)
File with the Postfix SMTP server RSA certificate in PEM format. This
file may also contain the Postfix SMTP server private RSA key.

Public Internet MX hosts without certificates signed by a "reputable"
CA must generate, and be prepared to present to most clients, a self-
signed or private-CA signed certificate. The client will not be able to
authenticate the server, but unless it is running Postfix 2.3 or simi-
lar software, it will still insist on a server certificate.

For servers that are not public Internet MX hosts, Postfix 2.3 supports
configurations with no certificates. This entails the use of just the
anonymous TLS ciphers, which are not supported by typical SMTP clients.
Since such clients will not, as a rule, fall back to plain text after a
TLS handshake failure, the server will be unable to receive email from
TLS enabled clients. To avoid accidental configurations with no cer-
tificates, Postfix 2.3 enables certificate-less operation only when the
administrator explicitly sets "smtpd_tls_cert_file = none". This
ensures that new Postfix configurations will not accidentally run with
no certificates.

Both RSA and DSA certificates are supported. When both types are
present, the cipher used determines which certificate will be presented
to the client. For Netscape and OpenSSL clients without special cipher
choices the RSA certificate is preferred.

To enable a remote SMTP client to verify the Postfix SMTP server cer-
tificate, the issuing CA certificates must be made available to the
client. You should include the required certificates in the server cer-
tificate file, the server certificate first, then the issuing CA(s)
(bottom-up order).

Example: the certificate for "server.example.com" was issued by "inter-
mediate CA" which itself has a certificate of "root CA". Create the
server.pem file with "cat server_cert.pem intermediate_CA.pem
root_CA.pem > server.pem".

If you also want to verify client certificates issued by these CAs, you
can add the CA certificates to the smtpd_tls_CAfile, in which case it
is not necessary to have them in the smtpd_tls_cert_file or
smtpd_tls_dcert_file.

A certificate supplied here must be usable as an SSL server certificate
and hence pass the "openssl verify -purpose sslserver ..." test.

Example:

smtpd_tls_cert_file = /etc/postfix/server.pem

This feature is available in Postfix 2.2 and later.

smtpd_tls_cipherlist (default: empty)
Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher
list. It is easy to create inter-operability problems by choosing a
non-default cipher list. Do not use a non-default TLS cipherlist for MX
hosts on the public Internet. Clients that begin the TLS handshake, but
are unable to agree on a common cipher, may not be able to send any
email to the SMTP server. Using a restricted cipher list may be more
appropriate for a dedicated MSA or an internal mailhub, where one can
exert some control over the TLS software and settings of the connecting
clients.

Note: do not use "" quotes around the parameter value.

This feature is available with Postfix version 2.2. It is not used with
Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead.

smtpd_tls_ciphers (default: export)
The minimum TLS cipher grade that the Postfix SMTP server will use with
opportunistic TLS encryption. Cipher types listed in
smtpd_tls_exclude_ciphers are excluded from the base definition of the
selected cipher grade. The default value "export" ensures maximum
inter-operability. Because encryption is optional, stronger controls
are not appropriate, and this setting SHOULD NOT be changed unless the
change is essential.

When TLS is mandatory the cipher grade is chosen via the
smtpd_tls_mandatory_ciphers configuration parameter, see there for syn-
tax details.

Example:
smtpd_tls_ciphers = export

This feature is available in Postfix 2.6 and later. With earlier Post-
fix releases only the smtpd_tls_mandatory_ciphers parameter is imple-
mented, and opportunistic TLS always uses "export" or better (i.e. all)
ciphers.

smtpd_tls_dcert_file (default: empty)
File with the Postfix SMTP server DSA certificate in PEM format. This
file may also contain the Postfix SMTP server private DSA key.

See the discussion under smtpd_tls_cert_file for more details.

Example:

smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)
File with DH parameters that the Postfix SMTP server should use with
EDH ciphers.

Instead of using the exact same parameter sets as distributed with
other TLS packages, it is more secure to generate your own set of
parameters with something like the following command:

openssl gendh -out /etc/postfix/dh_1024.pem -2 1024

Your actual source for entropy may differ. Some systems have /dev/ran-
dom; on other system you may consider using the "Entropy Gathering Dae-
mon EGD", available at http://egd.sourceforge.net/

Example:

smtpd_tls_dh1024_param_file = /etc/postfix/dh_1024.pem

This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)
File with DH parameters that the Postfix SMTP server should use with
EDH ciphers.

See also the discussion under the smtpd_tls_dh1024_param_file configu-
ration parameter.

Example:

smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
File with the Postfix SMTP server DSA private key in PEM format. This
file may be combined with the Postfix SMTP server DSA certificate file
specified with $smtpd_tls_dcert_file.

This feature is available in Postfix 2.2 and later.

smtpd_tls_eccert_file (default: empty)
File with the Postfix SMTP server ECDSA certificate in PEM format.
This file may also contain the Postfix SMTP server private ECDSA key.

See the discussion under smtpd_tls_cert_file for more details.

Example:

smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)
File with the Postfix SMTP server ECDSA private key in PEM format.
This file may be combined with the Postfix SMTP server ECDSA certifi-
cate file specified with $smtpd_tls_eccert_file.

This feature is available in Postfix 2.6 and later, when Postfix is
compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eecdh_grade (default: see postconf -d output)
The Postfix SMTP server security grade for ephemeral elliptic-curve
Diffie-Hellman (EECDH) key exchange.

The available choices are:

none Don't use EECDH. Ciphers based on EECDH key exchange will be
disabled. This is the default in official Postfix releases
(mail_version = major.minor.patchlevel).

strong Use EECDH with approximately 128 bits of security at a reason-
able computational cost. This is the current best-practice
trade-off between security and computational efficiency. This is
the default in Postfix snapshot releases (mail_version =
major.minor-releasedate).

ultra Use EECDH with approximately 192 bits of security at computa-
tional cost that is approximately twice as high as 128 bit
strength ECC. Barring significant progress in attacks on ellip-
tic curve crypto-systems, the "strong" curve is sufficient for
most users.

This feature is available in Postfix 2.6 and later, when it is compiled
and linked with OpenSSL 1.0.0 or later.

smtpd_tls_exclude_ciphers (default: empty)
List of ciphers or cipher types to exclude from the SMTP server cipher
list at all TLS security levels. Excluding valid ciphers can create
interoperability problems. DO NOT exclude ciphers unless it is essen-
tial to do so. This is not an OpenSSL cipherlist; it is a simple list
separated by whitespace and/or commas. The elements are a single
cipher, or one or more "+" separated cipher properties, in which case
only ciphers matching all the properties are excluded.

Examples (some of these will cause problems):

smtpd_tls_exclude_ciphers = aNULL
smtpd_tls_exclude_ciphers = MD5, DES
smtpd_tls_exclude_ciphers = DES+MD5
smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
smtpd_tls_exclude_ciphers = kEDH+aRSA

The first setting disables anonymous ciphers. The next setting disables
ciphers that use the MD5 digest algorithm or the (single) DES encryp-
tion algorithm. The next setting disables ciphers that use MD5 and DES
together. The next setting disables the two ciphers "AES256-SHA" and
"DES-CBC3-MD5". The last setting disables ciphers that use "EDH" key
exchange with RSA authentication.

This feature is available in Postfix 2.3 and later.

smtpd_tls_fingerprint_digest (default: md5)
The message digest algorithm used to construct client-certificate fin-
gerprints for check_ccert_access and permit_tls_clientcerts. The
default algorithm is md5, for backwards compatibility with Postfix
releases prior to 2.5.

While additional digest algorithms are often available with OpenSSL's
libcrypto, only those used by libssl in SSL cipher suites are available
to Postfix. For now this means just md5 or sha1.

To find the fingerprint of a specific certificate file, with a specific
digest algorithm, run:

$ openssl x509 -noout -fingerprint -digest -in certfile.pem

The text to the right of "=" sign is the desired fingerprint. For
example:

$ openssl x509 -noout -fingerprint -sha1 -in cert.pem
SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

Example: client-certificate access table, with sha1 fingerprints:

/etc/postfix/main.cf:
smtpd_tls_fingerprint_digest = sha1
smtpd_client_restrictions =
check_ccert_access hash:/etc/postfix/access,
reject
/etc/postfix/access:
# Action folded to next line...
AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
OK
85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
permit_auth_destination

This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)
File with the Postfix SMTP server RSA private key in PEM format. This
file may be combined with the Postfix SMTP server RSA certificate file
specified with $smtpd_tls_cert_file.

smtpd_tls_loglevel (default: 0)
Enable additional Postfix SMTP server logging of TLS activity. Each
logging level also includes the information that is logged at a lower
logging level.

0 Disable logging of TLS activity.

1 Log TLS handshake and certificate information.

2 Log levels during TLS negotiation.

3 Log hexadecimal and ASCII dump of TLS negotiation process.

4 Also log hexadecimal and ASCII dump of complete transmission
after STARTTLS.

Use "smtpd_tls_loglevel = 3" only in case of problems. Use of loglevel
4 is strongly discouraged.

This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)
The minimum TLS cipher grade that the Postfix SMTP server will use with
mandatory TLS encryption. The default grade ("medium") is sufficiently
strong that any benefit from globally restricting TLS sessions to a
more stringent grade is likely negligible, especially given the fact
that many implementations still do not offer any stronger ("high"
grade) ciphers, while those that do, will always use "high" grade
ciphers. So insisting on "high" grade ciphers is generally counter-pro-
ductive. Allowing "export" or "low" ciphers is typically not a good
idea, as systems limited to just these are limited to obsolete
browsers. No known SMTP clients fail to support at least one "medium"
or "high" grade cipher.

The following cipher grades are supported:

export Enable "EXPORT" grade or stronger OpenSSL ciphers. This is the
most appropriate setting for public MX hosts, and is always used
with opportunistic TLS encryption. The underlying cipherlist is
specified via the tls_export_cipherlist configuration parameter,
which you are strongly encouraged to not change.

low Enable "LOW" grade or stronger OpenSSL ciphers. The underlying
cipherlist is specified via the tls_low_cipherlist configuration
parameter, which you are strongly encouraged to not change.

medium Enable "MEDIUM" grade or stronger OpenSSL ciphers. These use
128-bit or longer symmetric bulk-encryption keys. This is the
default minimum strength for mandatory TLS encryption. The
underlying cipherlist is specified via the tls_medium_cipherlist
configuration parameter, which you are strongly encouraged to
not change.

high Enable only "HIGH" grade OpenSSL ciphers. The underlying
cipherlist is specified via the tls_high_cipherlist configura-
tion parameter, which you are strongly encouraged to not change.

null Enable only the "NULL" OpenSSL ciphers, these provide authenti-
cation without encryption. This setting is only appropriate in
the rare case that all clients are prepared to use NULL ciphers
(not normally enabled in TLS clients). The underlying cipherlist
is specified via the tls_null_cipherlist configuration parame-
ter, which you are strongly encouraged to not change.

Cipher types listed in smtpd_tls_mandatory_exclude_ciphers or
smtpd_tls_exclude_ciphers are excluded from the base definition of the
selected cipher grade. See smtpd_tls_ciphers for cipher controls that
apply to opportunistic TLS.

The underlying cipherlists for grades other than "null" include anony-
mous ciphers, but these are automatically filtered out if the server is
configured to ask for client certificates. You are very unlikely to
need to take any steps to exclude anonymous ciphers, they are excluded
automatically as required. If you must exclude anonymous ciphers even
when Postfix does not need or use peer certificates, set
"smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only
when TLS is enforced, set "smtpd_tls_mandatory_exclude_ciphers =
aNULL".

This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)
Additional list of ciphers or cipher types to exclude from the SMTP
server cipher list at mandatory TLS security levels. This list works in
addition to the exclusions listed with smtpd_tls_exclude_ciphers (see
there for syntax details).

This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: SSLv3, TLSv1)
The SSL/TLS protocols accepted by the Postfix SMTP server with manda-
tory TLS encryption. If the list is empty, the server supports all
available SSL/TLS protocol versions. A non-empty value is a list of
protocol names separated by whitespace, commas or colons. The supported
protocol names are "SSLv2", "SSLv3" and "TLSv1", and are not case sen-
sitive.

With Postfix >= 2.5 the parameter syntax is expanded to support proto-
col exclusions. One can now explicitly exclude SSLv2 by setting
"smtpd_tls_mandatory_protocols = !SSLv2". To exclude both SSLv2 and
SSLv3 set "smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3". Listing the
protocols to include, rather than protocols to exclude, is still sup-
ported, use the form you find more intuitive.

Example:

smtpd_tls_mandatory_protocols = TLSv1
# Alternative form with Postfix >= 2.5:
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3

This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: empty)
List of TLS protocols that the Postfix SMTP server will exclude or
include with opportunistic TLS encryption. This parameter SHOULD be
left at its default empty value, allowing all protocols to be used with
opportunistic TLS.

In main.cf the values are separated by whitespace, commas or colons. An
empty value means allow all protocols. The valid protocol names, (see
\fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1". In
smtp_tls_policy_maps table entries, "protocols" attribute values are
separated by a colon.

To include a protocol list its name, to exclude it, prefix the name
with a "!" character. To exclude SSLv2 even for opportunistic TLS set
"smtpd_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
"smtpd_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the proto-
cols to include, is supported, but not recommended. OpenSSL provides no
mechanisms for excluding protocols not known at compile-time. If Post-
fix is linked against an OpenSSL library that supports additional pro-
tocol versions, they cannot be excluded using either syntax.

Example:
smtpd_tls_protocols = !SSLv2

This feature is available in Postfix 2.6 and later.

smtpd_tls_received_header (default: no)
Request that the Postfix SMTP server produces Received: message head-
ers that include information about the protocol and cipher used, as
well as the client CommonName and client certificate issuer CommonName.
This is disabled by default, as the information may be modified in
transit through other mail servers. Only information that was recorded
by the final destination can be trusted.

This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)
With mandatory TLS encryption, require a trusted remote SMTP client
certificate in order to allow TLS connections to proceed. This option
implies "smtpd_tls_ask_ccert = yes".

When TLS encryption is optional, this setting is ignored with a warning
written to the mail log.

This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty)
The SMTP TLS security level for the Postfix SMTP server; when a non-
empty value is specified, this overrides the obsolete parameters
smtpd_use_tls and smtpd_enforce_tls. This parameter is ignored with
"smtpd_tls_wrappermode = yes".

Specify one of the following security levels:

none TLS will not be used.

may Opportunistic TLS: announce STARTTLS support to SMTP clients,
but do not require that clients use TLS encryption.

encrypt
Mandatory TLS encryption: announce STARTTLS support to SMTP
clients, and require that clients use TLS encryption. According
to RFC 2487 this MUST NOT be applied in case of a publicly-ref-
erenced SMTP server. Instead, this option should be used only on
dedicated servers.

Note 1: the "fingerprint", "verify" and "secure" levels are not sup-
ported here. The Postfix SMTP server logs a warning and uses "encrypt"
instead. To verify SMTP client certificates, see TLS_README for a dis-
cussion of the smtpd_tls_ask_ccert, smtpd_tls_req_ccert, and per-
mit_tls_clientcerts features.

Note 2: The parameter setting "smtpd_tls_security_level = encrypt"
implies "smtpd_tls_auth_only = yes".

Note 3: when invoked via "sendmail -bs", Postfix will never offer
STARTTLS due to insufficient privileges to access the server private
key. This is intended behavior.

This feature is available in Postfix 2.3 and later.

smtpd_tls_session_cache_database (default: empty)
Name of the file containing the optional Postfix SMTP server TLS ses-
sion cache. Specify a database type that supports enumeration, such as
btree or sdbm; there is no need to support concurrent access. The file
is created if it does not exist. The smtpd(8) daemon does not use this
parameter directly, rather the cache is implemented indirectly in the
tlsmgr(8) daemon. This means that per-smtpd-instance master.cf over-
rides of this parameter are not effective. Note, that each of the cache
databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data-
base, $smtp_tls_session_cache_database (and with Postfix 2.3 and later
$lmtp_tls_session_cache_database), needs to be stored separately. It is
not at this time possible to store multiple caches in a single data-
base.

Note: dbm databases are not suitable. TLS session objects are too
large.

Example:

smtpd_tls_session_cache_database = btree:/var/db/postfix/smtpd_scache

This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)
The expiration time of Postfix SMTP server TLS session cache informa-
tion. A cache cleanup is performed periodically every $smtpd_tls_ses-
sion_cache_timeout seconds. As with $smtpd_tls_session_cache_database,
this parameter is implemented in the tlsmgr(8) daemon and therefore
per-smtpd-instance master.cf overrides are not possible.

This feature is available in Postfix 2.2 and later.

smtpd_tls_wrappermode (default: no)
Run the Postfix SMTP server in the non-standard "wrapper" mode, instead
of using the STARTTLS command.

If you want to support this service, enable a special port in mas-
ter.cf, and specify "-o smtpd_tls_wrappermode=yes" on the SMTP server's
command line. Port 465 (smtps) was once chosen for this purpose.

This feature is available in Postfix 2.2 and later.

smtpd_use_tls (default: no)
Opportunistic TLS: announce STARTTLS support to SMTP clients, but do
not require that clients use TLS encryption.

Note: when invoked via "sendmail -bs", Postfix will never offer START-
TLS due to insufficient privileges to access the server private key.
This is intended behavior.

This feature is available in Postfix 2.2 and later. With Postfix 2.3
and later use smtpd_tls_security_level instead.

soft_bounce (default: no)
Safety net to keep mail queued that would otherwise be returned to the
sender. This parameter disables locally-generated bounces, and pre-
vents the Postfix SMTP server from rejecting mail permanently, by
changing 5xx reply codes into 4xx. However, soft_bounce is no cure for
address rewriting mistakes or mail routing mistakes.

Example:

soft_bounce = yes

stale_lock_time (default: 500s)
The time after which a stale exclusive mailbox lockfile is removed.
This is used for delivery to file or mailbox.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

stress (default: empty)
This feature is documented in the STRESS_README document.

This feature is available in Postfix 2.5 and later.

strict_7bit_headers (default: no)
Reject mail with 8-bit text in message headers. This blocks mail from
poorly written applications.

This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.

This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)
Enable both strict_7bit_headers and strict_8bitmime_body.

This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.

This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)
Reject 8-bit message body text without 8-bit MIME content encoding
information. This blocks mail from poorly written applications.

Unfortunately, this also rejects majordomo approval requests when the
included request contains valid 8-bit MIME mail, and it rejects bounces
from mailers that do not MIME encapsulate 8-bit content (for example,
bounces from qmail or from old versions of Postfix).

This feature should not be enabled on a general purpose mail server,
because it is likely to reject legitimate email.

This feature is available in Postfix 2.0 and later.

strict_mailbox_ownership (default: yes)
Defer delivery when a mailbox file is not owned by its recipient. The
default setting is not backwards compatible.

This feature is available in Postfix 2.5.3 and later.

strict_mime_encoding_domain (default: no)
Reject mail with invalid Content-Transfer-Encoding: information for the
message/* or multipart/* MIME content types. This blocks mail from
poorly written software.

This feature should not be enabled on a general purpose mail server,
because it will reject mail after a single violation.

This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)
Require that addresses received in SMTP MAIL FROM and RCPT TO commands
are enclosed with <>, and that those addresses do not contain RFC 822
style comments or phrases. This stops mail from poorly written soft-
ware.

By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL FROM
and RCPT TO addresses.

sun_mailtool_compatibility (default: no)
Obsolete SUN mailtool compatibility feature. Instead, use "mail-
box_delivery_lock = dotlock".

swap_bangpath (default: yes)
Enable the rewriting of "site!user" into "user@site". This is neces-
sary if your machine is connected to UUCP networks. It is enabled by
default.

Note: with Postfix version 2.2, message header address rewriting hap-
pens only when one of the following conditions is true:

· The message is received with the Postfix sendmail(1) command,

· The message is received from a network client that matches
$local_header_rewrite_clients,

· The message is received from the network, and the
remote_header_rewrite_domain parameter specifies a non-empty
value.

To get the behavior before Postfix version 2.2, specify
"local_header_rewrite_clients = static:all".

Example:

swap_bangpath = no

syslog_facility (default: mail)
The syslog facility of Postfix logging. Specify a facility as defined
in syslog.conf(5). The default facility is "mail".

Warning: a non-default syslog_facility setting takes effect only after
a Postfix process has completed initialization. Errors during process
initialization will be logged with the default facility. Examples are
errors while parsing the command line arguments, and errors while
accessing the Postfix main.cf configuration file.

syslog_name (default: see postconf -d output)
The mail system name that is prepended to the process name in syslog
records, so that "smtpd" becomes, for example, "postfix/smtpd".

Warning: a non-default syslog_name setting takes effect only after a
Postfix process has completed initialization. Errors during process
initialization will be logged with the default name. Examples are
errors while parsing the command line arguments, and errors while
accessing the Postfix main.cf configuration file.

tcp_windowsize (default: 0)
An optional workaround for routers that break TCP window scaling.
Specify a value > 0 and < 65536 to enable this feature. With Postfix
TCP servers (smtpd(8), qmqpd(8)), this feature is implemented by the
Postfix master(8) daemon.

To change this parameter without stopping Postfix, you need to first
terminate all Postfix TCP servers:

# postconf -e master_service_disable=inet
# postfix reload

This immediately terminates all processes that accept network connec-
tions. Next, you enable Postfix TCP servers with the updated tcp_win-
dowsize setting:

# postconf -e tcp_windowsize=65535 master_service_disable=
# postfix reload

If you skip these steps with a running Postfix system, then the
tcp_windowsize change will work only for Postfix TCP clients (smtp(8),
lmtp(8)).

This feature is available in Postfix 2.6 and later.

tls_append_default_CA (default: no)
Append the system-supplied default certificate authority certificates
to the ones specified with *_tls_CApath or *_tls_CAfile. The default
is "no"; this prevents Postfix from trusting third-party certificates
and giving them relay permission with permit_tls_all_clientcerts.

This feature is available in Postfix 2.4.15, 2.5.11, 2.6.8, 2.7.2 and
later versions. Specify "tls_append_default_CA = yes" for backwards
compatibility, to avoid breaking certificate verification with sites
that don't use permit_tls_all_clientcerts.

tls_daemon_random_bytes (default: 32)
The number of pseudo-random bytes that an smtp(8) or smtpd(8) process
requests from the tlsmgr(8) server in order to seed its internal pseudo
random number generator (PRNG). The default of 32 bytes (equivalent to
256 bits) is sufficient to generate a 128bit (or 168bit) session key.

This feature is available in Postfix 2.2 and later.

tls_eecdh_strong_curve (default: prime256v1)
The elliptic curve used by the SMTP server for sensibly strong
ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
server when "smtpd_tls_eecdh_grade = strong". The phrase "sensibly
strong" means approximately 128-bit security based on best known
attacks. The selected curve must be implemented by OpenSSL (as reported
by ecparam(1) with the "-list_curves" option) and be one of the curves
listed in Section 5.1.1 of RFC 4492. You should not generally change
this setting.

This default curve is specified in NSA "Suite B" Cryptography (see
http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for information
classified as SECRET.

Note: elliptic curve names are poorly standardized; different standards
groups are assigning different names to the same underlying curves.
The curve with the X9.62 name "prime256v1" is also known under the SECG
name "secp256r1", but OpenSSL does not recognize the latter name.

This feature is available in Postfix 2.6 and later, when it is compiled
and linked with OpenSSL 1.0.0 or later.

tls_eecdh_ultra_curve (default: secp384r1)
The elliptic curve used by the SMTP server for maximally strong
ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
server when "smtpd_tls_eecdh_grade = ultra". The phrase "maximally
strong" means approximately 192-bit security based on best known
attacks. This additional strength comes at a significant computational
cost, most users should instead set "smtpd_tls_eecdh_grade = strong".
The selected curve must be implemented by OpenSSL (as reported by
ecparam(1) with the "-list_curves" option) and be one of the curves
listed in Section 5.1.1 of RFC 4492. You should not generally change
this setting.

This default "ultra" curve is specified in NSA "Suite B" Cryptography
(see http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for information
classified as TOP SECRET.

This feature is available in Postfix 2.6 and later, when it is compiled
and linked with OpenSSL 1.0.0 or later.

tls_export_cipherlist (default: ALL:+RC4:@STRENGTH)
The OpenSSL cipherlist for "EXPORT" or higher grade ciphers. This
defines the meaning of the "export" setting in smtpd_tls_manda-
tory_ciphers, smtp_tls_mandatory_ciphers and lmtp_tls_manda-
tory_ciphers. This is the cipherlist for the opportunistic ("may") TLS
client security level and is the default cipherlist for the SMTP
server. You are strongly encouraged to not change this setting. With
OpenSSL 1.0.0 and later the cipherlist may start with an "aNULL:" pre-
fix, which restores the 0.9.8-compatible ordering of the aNULL ciphers
to the top of the list when they are enabled. This prefix is not needed
with previous OpenSSL releases.

This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
The OpenSSL cipherlist for "HIGH" grade ciphers. This defines the mean-
ing of the "high" setting in smtpd_tls_mandatory_ciphers,
smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. You are
strongly encouraged to not change this setting. With OpenSSL 1.0.0 and
later the cipherlist may start with an "aNULL:" prefix, which restores
the 0.9.8-compatible ordering of the aNULL ciphers to the top of the
list when they are enabled. This prefix is not needed with previous
OpenSSL releases.

This feature is available in Postfix 2.3 and later.

tls_low_cipherlist (default: ALL:!EXPORT:+RC4:@STRENGTH)
The OpenSSL cipherlist for "LOW" or higher grade ciphers. This defines
the meaning of the "low" setting in smtpd_tls_mandatory_ciphers,
smtp_tls_mandatory_ciphers and lmtp_tls_mandatory_ciphers. You are
strongly encouraged to not change this setting. With OpenSSL 1.0.0 and
later the cipherlist may start with an "aNULL:" prefix, which restores
the 0.9.8-compatible ordering of the aNULL ciphers to the top of the
list when they are enabled. This prefix is not needed with previous
OpenSSL releases.

This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
The OpenSSL cipherlist for "MEDIUM" or higher grade ciphers. This
defines the meaning of the "medium" setting in smtpd_tls_manda-
tory_ciphers, smtp_tls_mandatory_ciphers and lmtp_tls_manda-
tory_ciphers. This is the default cipherlist for mandatory TLS encryp-
tion in the TLS client (with anonymous ciphers disabled when verifying
server certificates). You are strongly encouraged to not change this
setting. With OpenSSL 1.0.0 and later the cipherlist may start with an
"aNULL:" prefix, which restores the 0.9.8-compatible ordering of the
aNULL ciphers to the top of the list when they are enabled. This prefix
is not needed with previous OpenSSL releases.

This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)
The OpenSSL cipherlist for "NULL" grade ciphers that provide authenti-
cation without encryption. This defines the meaning of the "null" set-
ting in smtpd_mandatory_tls_ciphers, smtp_tls_mandatory_ciphers and
lmtp_tls_mandatory_ciphers. You are strongly encouraged to not change
this setting.

This feature is available in Postfix 2.3 and later.

tls_random_bytes (default: 32)
The number of bytes that tlsmgr(8) reads from $tls_random_source when
(re)seeding the in-memory pseudo random number generator (PRNG) pool.
The default of 32 bytes (256 bits) is good enough for 128bit symmetric
keys. If using EGD or a device file, a maximum of 255 bytes is read.

This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: see postconf -d output)
Name of the pseudo random number generator (PRNG) state file that is
maintained by tlsmgr(8). The file is created when it does not exist,
and its length is fixed at 1024 bytes.

As of version 2.5, Postfix no longer uses root privileges when opening
this file, and the default file location was changed from ${con-
fig_directory}/prng_exch to ${data_directory}/prng_exch. As a migra-
tion aid, an attempt to open the file under a non-Postfix directory is
redirected to the Postfix-owned data_directory, and a warning is
logged.

This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)
The time between attempts by tlsmgr(8) to save the state of the pseudo
random number generator (PRNG) to the file specified with $tls_ran-
dom_exchange_name.

This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)
The maximal time between attempts by tlsmgr(8) to re-seed the in-memory
pseudo random number generator (PRNG) pool from external sources. The
actual time between re-seeding attempts is calculated using the PRNG,
and is between 0 and the time specified.

This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)
The external entropy source for the in-memory tlsmgr(8) pseudo random
number generator (PRNG) pool. Be sure to specify a non-blocking source.
If this source is not a regular file, the entropy source type must be
prepended: egd:/path/to/egd_socket for a source with EGD compatible
socket interface, or dev:/path/to/device for a device file.

Note: on OpenBSD systems specify /dev/arandom when /dev/urandom gives
timeout errors.

This feature is available in Postfix 2.2 and later.

trace_service_name (default: trace)
The name of the trace service. This service is implemented by the
bounce(8) daemon and maintains a record of mail deliveries and produces
a mail delivery report when verbose delivery is requested with "send-
mail -v".

This feature is available in Postfix 2.1 and later.

transport_delivery_slot_cost (default: $default_delivery_slot_cost)
A transport-specific override for the default_delivery_slot_cost param-
eter value, where transport is the master.cf name of the message deliv-
ery transport.

transport_delivery_slot_discount (default: $default_delivery_slot_discount)
A transport-specific override for the default_delivery_slot_discount
parameter value, where transport is the master.cf name of the message
delivery transport.

transport_delivery_slot_loan (default: $default_delivery_slot_loan)
A transport-specific override for the default_delivery_slot_loan param-
eter value, where transport is the master.cf name of the message deliv-
ery transport.

transport_destination_concurrency_failed_cohort_limit (default: $default_des-
tination_concurrency_failed_cohort_limit)
A transport-specific override for the default_destination_concur-
rency_failed_cohort_limit parameter value, where transport is the mas-
ter.cf name of the message delivery transport.

This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_limit (default: $default_destination_concur-
rency_limit)
A transport-specific override for the default_destination_concur-
rency_limit parameter value, where transport is the master.cf name of
the message delivery transport.

transport_destination_concurrency_negative_feedback (default: $default_desti-
nation_concurrency_negative_feedback)
A transport-specific override for the default_destination_concur-
rency_negative_feedback parameter value, where transport is the mas-
ter.cf name of the message delivery transport.

This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_positive_feedback (default: $default_desti-
nation_concurrency_positive_feedback)
A transport-specific override for the default_destination_concur-
rency_positive_feedback parameter value, where transport is the mas-
ter.cf name of the message delivery transport.

This feature is available in Postfix 2.5 and later.

transport_destination_rate_delay (default: $default_destination_rate_delay)
A transport-specific override for the default_destination_rate_delay
parameter value, where transport is the master.cf name of the message
delivery transport.

This feature is available in Postfix 2.5 and later.

transport_destination_recipient_limit (default: $default_destination_recipi-
ent_limit)
A transport-specific override for the default_destination_recipi-
ent_limit parameter value, where transport is the master.cf name of the
message delivery transport.

transport_extra_recipient_limit (default: $default_extra_recipient_limit)
A transport-specific override for the default_extra_recipient_limit
parameter value, where transport is the master.cf name of the message
delivery transport.

transport_initial_destination_concurrency (default: $initial_destination_con-
currency)
A transport-specific override for the initial_destination_concurrency
parameter value, where transport is the master.cf name of the message
delivery transport.

This feature is available in Postfix 2.5 and later.

transport_maps (default: empty)
Optional lookup tables with mappings from recipient address to (message
delivery transport, next-hop destination). See transport(5) for
details.

Specify zero or more "type:table" lookup tables. If you use this fea-
ture with local files, run "postmap /etc/postfix/transport" after mak-
ing a change.

For safety reasons, as of Postfix 2.3 this feature does not allow $num-
ber substitutions in regular expression maps.

Examples:

transport_maps = dbm:/etc/postfix/transport
transport_maps = hash:/etc/postfix/transport

transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)
A transport-specific override for the default_minimum_delivery_slots
parameter value, where transport is the master.cf name of the message
delivery transport.

transport_recipient_limit (default: $default_recipient_limit)
A transport-specific override for the default_recipient_limit parameter
value, where transport is the master.cf name of the message delivery
transport.

transport_recipient_refill_delay (default: $default_recipient_refill_delay)
A transport-specific override for the default_recipient_refill_delay
parameter value, where transport is the master.cf name of the message
delivery transport.

This feature is available in Postfix 2.4 and later.

transport_recipient_refill_limit (default: $default_recipient_refill_limit)
A transport-specific override for the default_recipient_refill_limit
parameter value, where transport is the master.cf name of the message
delivery transport.

This feature is available in Postfix 2.4 and later.

transport_retry_time (default: 60s)
The time between attempts by the Postfix queue manager to contact a
malfunctioning message delivery transport.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

transport_time_limit (default: $command_time_limit)
A transport-specific override for the command_time_limit parameter
value, where transport is the master.cf name of the message delivery
transport.

trigger_timeout (default: 10s)
The time limit for sending a trigger to a Postfix daemon (for example,
the pickup(8) or qmgr(8) daemon). This time limit prevents programs
from getting stuck when the mail system is under heavy load.

Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
The default time unit is s (seconds).

undisclosed_recipients_header (default: To: undisclosed-recipients:;)
Message header that the Postfix cleanup(8) server inserts when a mes-
sage contains no To: or Cc: message header. With Postfix 2.4 and later,
specify an empty value to disable this feature.

unknown_address_reject_code (default: 450)
The numerical Postfix SMTP server response code when a sender or recip-
ient address is rejected by the reject_unknown_sender_domain or
reject_unknown_recipient_domain restriction. The response is always
450 in case of a temporary DNS error.

Do not change this unless you have a complete understanding of RFC
2821.

unknown_address_tempfail_action (default: $reject_tempfail_action)
The Postfix SMTP server's action when reject_unknown_sender_domain or
reject_unknown_recipient_domain fail due to a temporary error condi-
tion. Specify "defer" to defer the remote SMTP client request immedi-
ately. With the default "defer_if_permit" action, the Postfix SMTP
server continues to look for opportunities to reject mail, and defers
the client request only if it would otherwise be accepted.

This feature is available in Postfix 2.6 and later.

unknown_client_reject_code (default: 450)
The numerical Postfix SMTP server response code when a client without
valid address <=> name mapping is rejected by the
reject_unknown_client_hostname restriction. The SMTP server always
replies with 450 when the mapping failed due to a temporary error con-
dition.

Do not change this unless you have a complete understanding of RFC
2821.

unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action)
The Postfix SMTP server's action when reject_unknown_helo_hostname
fails due to an temporary error condition. Specify "defer" to defer the
remote SMTP client request immediately. With the default "defer_if_per-
mit" action, the Postfix SMTP server continues to look for opportuni-
ties to reject mail, and defers the client request only if it would
otherwise be accepted.

This feature is available in Postfix 2.6 and later.

unknown_hostname_reject_code (default: 450)
The numerical Postfix SMTP server response code when the hostname spec-
ified with the HELO or EHLO command is rejected by the
reject_unknown_helo_hostname restriction.

Do not change this unless you have a complete understanding of RFC
2821.

unknown_local_recipient_reject_code (default: 550)
The numerical Postfix SMTP server response code when a recipient
address is local, and $local_recipient_maps specifies a list of lookup
tables that does not match the recipient. A recipient address is local
when its domain matches $mydestination, $proxy_interfaces or
$inet_interfaces.

The default setting is 550 (reject mail) but it is safer to initially
use 450 (try again later) so you have time to find out if your
local_recipient_maps settings are OK.

Example:

unknown_local_recipient_reject_code = 450

This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)
The numerical Postfix SMTP server reply code when a recipient address
matches $relay_domains, and relay_recipient_maps specifies a list of
lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)
The SMTP server reply code when a recipient address matches $vir-
tual_alias_domains, and $virtual_alias_maps specifies a list of lookup
tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)
The SMTP server reply code when a recipient address matches $vir-
tual_mailbox_domains, and $virtual_mailbox_maps specifies a list of
lookup tables that does not match the recipient address.

This feature is available in Postfix 2.0 and later.

unverified_recipient_defer_code (default: 450)
The numerical Postfix SMTP server response when a recipient address
probe fails due to a temporary error condition.

Unlike elsewhere in Postfix, you can specify 250 in order to accept the
address anyway.

Do not change this unless you have a complete understanding of RFC
2821.

This feature is available in Postfix 2.6 and later.

unverified_recipient_reject_code (default: 450)
The numerical Postfix SMTP server response when a recipient address is
rejected by the reject_unverified_recipient restriction.

Unlike elsewhere in Postfix, you can specify 250 in order to accept the
address anyway.

Do not change this unless you have a complete understanding of RFC
2821.

This feature is available in Postfix 2.1 and later.

unverified_recipient_reject_reason (default: empty)
The Postfix SMTP server's reply when rejecting mail with reject_unveri-
fied_recipient. Do not include the numeric SMTP reply code or the
enhanced status code. By default, the response includes actual address
verification details.

Example:

unverified_recipient_reject_reason = Recipient address lookup failed

This feature is available in Postfix 2.6 and later.

unverified_recipient_tempfail_action (default: $reject_tempfail_action)
The Postfix SMTP server's action when reject_unverified_recipient fails
due to a temporary error condition. Specify "defer" to defer the remote
SMTP client request immediately. With the default "defer_if_permit"
action, the Postfix SMTP server continues to look for opportunities to
reject mail, and defers the client request only if it would otherwise
be accepted.

This feature is available in Postfix 2.6 and later.

unverified_sender_defer_code (default: 450)
The numerical Postfix SMTP server response code when a sender address
probe fails due to a temporary error condition.

Unlike elsewhere in Postfix, you can specify 250 in order to accept the
address anyway.

Do not change this unless you have a complete understanding of RFC
2821.

This feature is available in Postfix 2.6 and later.

unverified_sender_reject_code (default: 450)
The numerical Postfix SMTP server response code when a recipient
address is rejected by the reject_unverified_sender restriction.

Unlike elsewhere in Postfix, you can specify 250 in order to accept the
address anyway.

Do not change this unless you have a complete understanding of RFC
2821.

This feature is available in Postfix 2.1 and later.

unverified_sender_reject_reason (default: empty)
The Postfix SMTP server's reply when rejecting mail with reject_unveri-
fied_sender. Do not include the numeric SMTP reply code or the enhanced
status code. By default, the response includes actual address verifica-
tion details.

Example:

unverified_sender_reject_reason = Sender address lookup failed

This feature is available in Postfix 2.6 and later.

unverified_sender_tempfail_action (default: $reject_tempfail_action)
The Postfix SMTP server's action when reject_unverified_sender fails
due to a temporary error condition. Specify "defer" to defer the remote
SMTP client request immediately. With the default "defer_if_permit"
action, the Postfix SMTP server continues to look for opportunities to
reject mail, and defers the client request only if it would otherwise
be accepted.

This feature is available in Postfix 2.6 and later.

verp_delimiter_filter (default: -=+)
The characters Postfix accepts as VERP delimiter characters on the
Postfix sendmail(1) command line and in SMTP commands.

This feature is available in Postfix 1.1 and later.

virtual_alias_domains (default: $virtual_alias_maps)
Postfix is final destination for the specified list of virtual alias
domains, that is, domains for which all addresses are aliased to
addresses in other local or remote domains. The SMTP server validates
recipient addresses with $virtual_alias_maps and rejects non-existent
recipients. See also the virtual alias domain class in the
ADDRESS_CLASS_README file

This feature is available in Postfix 2.0 and later. The default value
is backwards compatible with Postfix version 1.1.

The default value is $virtual_alias_maps so that you can keep all
information about virtual alias domains in one place. If you have many
users, it is better to separate information that changes more fre-
quently (virtual address -> local or remote address mapping) from
information that changes less frequently (the list of virtual domain
names).

Specify a list of host or domain names, "/file/name" or "type:table"
patterns, separated by commas and/or whitespace. A "/file/name" pattern
is replaced by its contents; a "type:table" lookup table is matched
when a table entry matches a lookup string (the lookup result is
ignored). Continue long lines by starting the next line with white-
space. Specify "!pattern" to exclude a host or domain name from the
list. The form "!/file/name" is supported only in Postfix version 2.4
and later.

See also the VIRTUAL_README and ADDRESS_CLASS_README documents for fur-
ther information.

Example:

virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)
The maximal number of addresses that virtual alias expansion produces
from each original recipient.

This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)
Optional lookup tables that alias specific mail addresses or domains to
other local or remote address. The table format and lookups are docu-
mented in virtual(5). For an overview of Postfix address manipulations
see the ADDRESS_REWRITING_README document.

This feature is available in Postfix 2.0 and later. The default value
is backwards compatible with Postfix version 1.1.

If you use this feature with indexed files, run "postmap /etc/post-
fix/virtual" after changing the file.

Examples:

virtual_alias_maps = dbm:/etc/postfix/virtual
virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_recursion_limit (default: 1000)
The maximal nesting depth of virtual alias expansion. Currently the
recursion limit is applied only to the left branch of the expansion
graph, so the depth of the tree can in the worst case reach the sum of
the expansion and recursion limits. This may change in the future.

This feature is available in Postfix 2.1 and later.

virtual_destination_concurrency_limit (default: $default_destination_concur-
rency_limit)
The maximal number of parallel deliveries to the same destination via
the virtual message delivery transport. This limit is enforced by the
queue manager. The message delivery transport name is the first field
in the entry in the master.cf file.

virtual_destination_recipient_limit (default: $default_destination_recipi-
ent_limit)
The maximal number of recipients per message for the virtual message
delivery transport. This limit is enforced by the queue manager. The
message delivery transport name is the first field in the entry in the
master.cf file.

Setting this parameter to a value of 1 changes the meaning of vir-
tual_destination_concurrency_limit from concurrency per domain into
concurrency per recipient.

virtual_gid_maps (default: empty)
Lookup tables with the per-recipient group ID for virtual(8) mailbox
delivery.

In a lookup table, specify a left-hand side of "@domain.tld" to match
any user in the specified domain that does not have a specific
"user@domain.tld" entry.

When a recipient address has an optional address extension
(user+foo@domain.tld), the virtual(8) delivery agent looks up the full
address first, and when the lookup fails, it looks up the unextended
address (user@domain.tld).

Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression lookup
tables, because that would open a security hole.

Note 2: for security reasons, the virtual(8) delivery agent will
silently ignore requests to use the proxymap(8) server. Instead it will
open the table directly. Before Postfix version 2.2, the virtual(8)
delivery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)
A prefix that the virtual(8) delivery agent prepends to all pathname
results from $virtual_mailbox_maps table lookups. This is a safety
measure to ensure that an out of control map doesn't litter the file
system with mailboxes. While virtual_mailbox_base could be set to "/",
this setting isn't recommended.

Example:

virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)
Postfix is final destination for the specified list of domains; mail is
delivered via the $virtual_transport mail delivery transport. By
default this is the Postfix virtual(8) delivery agent. The SMTP server
validates recipient addresses with $virtual_mailbox_maps and rejects
mail for non-existent recipients. See also the virtual mailbox domain
class in the ADDRESS_CLASS_README file.

This parameter expects the same syntax as the mydestination configura-
tion parameter.

This feature is available in Postfix 2.0 and later. The default value
is backwards compatible with Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)
The maximal size in bytes of an individual virtual(8) mailbox or
maildir file, or zero (no limit).

virtual_mailbox_lock (default: see postconf -d output)
How to lock a UNIX-style virtual(8) mailbox before attempting delivery.
For a list of available file locking methods, use the "postconf -l"
command.

This setting is ignored with maildir style delivery, because such
deliveries are safe without application-level locks.

Note 1: the dotlock method requires that the recipient UID or GID has
write access to the parent directory of the recipient's mailbox file.

Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)
Optional lookup tables with all valid addresses in the domains that
match $virtual_mailbox_domains.

In a lookup table, specify a left-hand side of "@domain.tld" to match
any user in the specified domain that does not have a specific
"user@domain.tld" entry.

The virtual(8) delivery agent uses this table to look up the per-recip-
ient mailbox or maildir pathname. If the lookup result ends in a slash
("/"), maildir-style delivery is carried out, otherwise the path is
assumed to specify a UNIX-style mailbox file. Note that $virtual_mail-
box_base is unconditionally prepended to this path.

Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression lookup
tables, because that would open a security hole.

virtual_maps (default: empty)
Optional lookup tables with a) names of domains for which all addresses
are aliased to addresses in other local or remote domains, and b)
addresses that are aliased to addresses in other local or remote
domains. Available before Postfix version 2.0. With Postfix version
2.0 and later, this is replaced by separate controls: vir-
tual_alias_domains and virtual_alias_maps.

virtual_minimum_uid (default: 100)
The minimum user ID value that the virtual(8) delivery agent accepts as
a result from $virtual_uid_maps table lookup. Returned values less
than this will be rejected, and the message will be deferred.

virtual_transport (default: virtual)
The default mail delivery transport and next-hop destination for final
delivery to domains listed with $virtual_mailbox_domains. This infor-
mation can be overruled with the transport(5) table.

This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)
Lookup tables with the per-recipient user ID that the virtual(8) deliv-
ery agent uses while writing to the recipient's mailbox.

In a lookup table, specify a left-hand side of "@domain.tld" to match
any user in the specified domain that does not have a specific
"user@domain.tld" entry.

Note 1: for security reasons, the virtual(8) delivery agent disallows
regular expression substitution of $1 etc. in regular expression lookup
tables, because that would open a security hole.