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 logical 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.

    •   The expression "${name:value}" expands to "value" when "$name" is empty.

•   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 configuration 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 configuration 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_reject_code (default: 554)
The numerical Postfix SMTP server response code when a client is rejected by an access(5) map restriction.

Do not change this unless you have a complete understanding of RFC 821.

address_verify_default_transport (default: $default_transport)
Overrides the default_transport parameter setting for address verification 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 verification probes.

This feature is available in Postfix 2.1 and later.

address_verify_map (default: empty)
Optional 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.

By default, the information is kept in volatile memory, and is lost after "postfix reload" or "postfix stop".

Specify a location in a file system that will not fill up. If the database becomes corrupted, the world comes to an end. To recover delete the file and do "postfix reload".

Examples:

address_verify_map = hash:/usr/local/etc/postfix/verify
address_verify_map = btree:/usr/local/etc/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 verification 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: 3)
How many times to query the verify(8) service for the completion of an address verification request in progress.

The default poll count is 3.

Specify 1 to implement a crude form of greylisting, that is, always defer the first delivery request for a never seen before address.

Example:

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 verification 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 verification 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 feature is available in Postfix 2.1 and later.

address_verify_sender (default: postmaster)
The sender address to use in address verification probes. 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_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 verification 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.

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, respectively.

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 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.

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

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-specified 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 directory, and is used by set-gid Postfix commands such as postqueue(1) and postdrop(1).

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.

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 not part of the stable Postfix 2.1 release.

The default interval is relatively short. Because of the high frequency of updates, the anvil(8) server uses volatile memory only. Thus, information 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 implemented by the anvil(8) service which is not part of the stable Postfix 2.1 release.

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

append_at_myorigin (default: yes)
Append the string "@$myorigin" to mail addresses without domain information.

This feature is enabled by default and must not be turned off. Postfix does not support domain-less addresses.

append_dot_mydomain (default: yes)
Append the string ".$mydomain" to addresses that have no ".domain" information.

This feature is enabled by default. If disabled, users will not be able to send mail to "user@partialdomainname" but will have to specify full domain names instead.

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_verp_clients (default: $mynetworks)
What SMTP clients are allowed to specify the XVERP command. This command 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 version 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.

backwards_bounce_logfile_compatibility (default: yes)
Produce additional bounce(8) logfile records that can be read by older Postfix versions. The current and more extensible "name = value" format is needed in order to implement more sophisticated functionality.

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, $virtual_alias_domains, or $virtual_mailbox_domains. By default, the Postfix SMTP client returns such mail as undeliverable.

Specify, for example, "best_mx_transport = local" to pass the mail from the 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" 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.

broken_sasl_auth_clients (default: no)
Enable inter-operability with SMTP clients that implement an obsolete version of the AUTH command (RFC 2554). 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_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. This is typically used to clean up dirty addresses from legacy mail systems, or to replace login names by Firstname.Lastname. The table format and lookups are documented in canonical(5).

If you use this feature, run "postmap /usr/local/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.

Examples:

canonical_maps = dbm:/usr/local/etc/postfix/canonical
canonical_maps = hash:/usr/local/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_expansion_filter (default: see postconf -d output)
Restrict the characters that the local(8) delivery agent allows in $name expansions of $mailbox_command. 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 commands).

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

With Postfix command that run with set-gid privileges, a config_directory 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.

content_filter (default: empty)
The name of a mail delivery transport that filters mail after it is queued.

This parameter uses the same syntax as the right-hand side of a Postfix transport(5) table. This setting has a lower precedence than a content filter that is specified with an access(5) table or in a header_checks(5) or body_checks(5) table.

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).

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 result from lookup tables is ignored.

Pattern matching of domain names is controlled by the parent_domain_matches_subdomains parameter.

Examples:

debug_peer_list = 127.0.0.1
debug_peer_list = some.domain

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
    xxgdb $daemon_directory/$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 maximum, 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.

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 settings.

This parameter speeds up the moment when a message preemption can happen. Instead of waiting until the full amount of delivery slots required is available, the preemption can happen when transport_delivery_slot_discount percent of the required amount plus transport_delivery_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.

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

This parameter speeds up the moment when a message preemption can happen. Instead of waiting until the full amount of delivery slots required is available, the preemption can happen when transport_delivery_slot_discount percent of the required amount plus transport_delivery_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.

default_destination_concurrency_limit (default: 20)
The default maximal number of parallel deliveries to the same destination. This is the default limit for delivery via the lmtp(8), pipe(8), smtp(8) and virtual(8) delivery agents.

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 corresponding per-destination concurrency limit from concurrency per domain into concurrency per recipient.

default_extra_recipient_limit (default: 1000)
The default value for the extra per-transport limit imposed on the number 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.

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.

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 delivery 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".

$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.

$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).

default_recipient_limit (default: 10000)
The default per-transport upper limit on the number of in-memory recipients. These limits take priority over the global qmgr_message_recipient_limit after the message has been assigned to the respective transports. See also default_extra_recipient_limit and qmgr_message_recipient_minimum.

default_transport (default: smtp)
The default mail delivery transport for domains 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 transport(5) table.

Specify a string of the form transport:nexthop, where transport is the name of a mail delivery transport defined in master.cf. The :nexthop part is optional. For more details see the transport(5) manual page.

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 821.

defer_service_name (default: defer)
The name of the defer(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.

defer_transports (default: empty)
The names of message delivery transports that should not be delivered to 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_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 integral value.

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 mailbox 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).

disable_dns_lookups (default: no)
Disable DNS lookups in the Postfix SMTP and LMTP clients. When disabled, hosts are looked up with the gethostbyname() system library routine 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 special 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 harvest 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_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.

enable_errors_to (default: no)
Report mail delivery errors to the address specified with the non-standard Errors-To: message header, instead of the envelope sender address. This support is disabled by default with Postfix 2.1 and later, 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, rewritten recipient), and generates non-empty original recipient queue file records.

When this parameter is set to no, the cleanup(8) daemon performs duplicate 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 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.

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 whitespace or comma. The name=value form is supported with Postfix 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 2.1.

fallback_relay (default: empty)
Optional list of relay hosts for SMTP destinations that can't be found or that are unreachable.

By default, mail is returned to the sender when a destination is not found, and delivery is deferred if 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, Postfix will try them in the specified order.

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) database or in the UNIX passwd database.

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 destinations 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: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 the domain or its parent domain appears as lookup key.

Specify "fast_flush_domains =" 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 letter 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 letter 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-destination 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.

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 expansions are done on forward_path before the search actually happens:

$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

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, execute the command "postfix reload".

hash_queue_names (default: see postconf -d output)
The names of queue directories that are split across multiple subdirectory levels.

After changing the hash_queue_names or hash_queue_depth parameter, execute 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 message 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 "/" for qmail-style delivery.

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

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, configure 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 Postfix 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 whitespace or comma. The name=value form is supported with Postfix 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. By default, the software claims all active interfaces on the machine. The parameter also controls delivery of mail to user@[ip.address].

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

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

initial_destination_concurrency (default: 5)
The initial per-destination concurrency level for parallel delivery to the same destination. This limit applies to delivery via smtp(8), and via the pipe(8) and virtual(8) delivery agents.

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

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_hostname restriction.

Do not change this unless you have a complete understanding of RFC 821.

ipc_idle (default: 100s)
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.

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 situations. 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_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.

The effectiveness of cached connections will be determined by the number 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 specified 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 configuration 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_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_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_destination_concurrency_limit (default: $default_destination_concurrency_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_recipient_limit)
The maximal number of recipients per delivery 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.

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

lmtp_lhlo_timeout (default: 300s)
The LMTP client time limit for receiving the LMTP greeting banner. When the server drops the connection without sending a greeting banner, or when it sends no greeting banner 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).

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_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_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_rset_timeout (default: 120s)
The LMTP client time limit for sending the RSET command, and for receiving the server response. The LMTP client sends RSET in order to find out if 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_enable (default: no)
Enable SASL authentication in the Postfix LMTP client.

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_security_options (default: noplaintext, noanonymous)
What authentication mechanisms the Postfix LMTP client is allowed to use. The list of available authentication mechanisms is system dependent.

noplaintext
    Disallow authentication methods that use plaintext passwords.

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

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

noanonymous
    Disallow anonymous logins.

Example:

lmtp_sasl_security_options = noplaintext

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

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

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_recipient_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_destination_concurrency_limit from concurrency per recipient into concurrency per domain.

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
Lookup tables with all names or addresses of local recipients: a recipient 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, specify "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_recipient_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 "fallback_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 for domains that match $mydestination, $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.

Specify a string of the form transport:nexthop, where transport is the name of a mail delivery transport defined in master.cf. The :nexthop part is optional. For more details see the transport(5) manual page.

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 $mydestination, $inet_interfaces or $proxy_interfaces is returned as undeliverable.

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 processes on the system. In particular, don't specify nobody or daemon. PLEASE USE A DEDICATED USER ID AND GROUP ID.

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. Postfix 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 primary group ID privileges of the recipient. Exception: command delivery for root executes with $default_privs privileges. This is not a problem, 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:

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.

RECIPIENT
    The full recipient address.

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.

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

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.

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

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.

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

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 821.

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

Example:

masquerade_domains = $mydomain

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

By default, address masquerading makes no exceptions.

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. Specify "!name" to exclude a name from the list. 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). Continue long lines by starting the next line with whitespace.

Examples:

masquerade_exceptions = root, mailer-daemon
masquerade_exceptions = root

max_idle (default: 100s)
The maximum amount of time that an idle Postfix daemon process waits for the next service request before exiting. This parameter is ignored by the Postfix queue manager.

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 connection requests before a Postfix daemon process terminates. 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.

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 undeliverable.

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

mime_boundary_length_limit (default: 2048)
The maximal length of MIME multipart boundary strings. The MIME processor is unable to distinguish between boundary strings that do not differ 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 nesting level of multipart mail that the MIME processor will handle. Postfix refuses mail that is nested deeper.

This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 1000s)
The minimal time between attempts to deliver a deferred message. This parameter also limits the time an unreachable destination is kept in the short-term, in-memory, destination status cache.

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

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 restriction.

Do not change this unless you have a complete understanding of RFC 821.

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_recipient_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.

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 name matches a lookup key (the lookup result is ignored). Continue long lines by starting the next line with whitespace.

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.domain.tld

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 description of the mynetworks_style parameter for more information.

Alternatively, you can specify the mynetworks list by hand, in which case Postfix ignores the mynetworks_style setting.

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 "/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.

Examples:

mynetworks = 168.100.189.0/28, 127.0.0.0/8
mynetworks = $config_directory/mynetworks
mynetworks = hash:/usr/local/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 adequate 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 headers 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_hostname, reject_non_fqdn_sender or reject_non_fqdn_recipient restriction.

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.

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: postmaster).

2bounce
    Send undeliverable bounced mail to the postmaster. The notification is sent to the address specified with the 2bounce_notice_recipient configuration parameter (default: postmaster).

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: postmaster).

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

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 configuration 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.

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.

prepend_delivered_header (default: command, file, forward)
The message delivery contexts where the Postfix local(8) delivery agent prepends a Delivered-To: message header.

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@domain -> joe.user", the address "joe+foo@domain" would rewrite to "joe.user+foo".

Specify zero or more of canonical, virtual, alias, forward or include. These cause address extension propagation with canonical(5), virtual(5), and aliases(5) maps, and with local(8) .forward and :include: file lookups, 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. Table references that don't begin with proxy: are ignored. The proxymap(8) table accesses are read-only.

This feature is available in Postfix 2.0 and later.

qmgr_clog_warn_time (default: 300s)
The minimal delay between warnings that a specific destination is clogging 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 non-file name pattern with an exclamation point (!).

Example:

qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

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 seconds 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 2.1 SMTP server rejects MAIL FROM commands when the amount of free space is less than 1.5*$message_size_limit. To specify a higher minimum free space limit, specify a queue_minfree value that is at least 1.5*$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: 1000s)
The time between deferred queue scans by the queue manager.

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 parameter. 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, configure or operate a specific Postfix subsystem or feature.

receive_override_options (default: empty)
Enable or disable recipient validation, built-in content filtering, or address rewriting. Typically, these are specified in master.cf as command-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 content filter.

no_header_body_checks
    Disable header/body_checks. 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 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 recipient 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 /usr/local/etc/postfix/recipient_bcc".

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

Example:

recipient_bcc_maps = hash:/usr/local/etc/postfix/recipient_bcc

recipient_canonical_maps (default: empty)
Optional address mapping lookup tables for envelope and header recipient addresses. The table format and lookups are documented in canonical(5).

Note: $recipient_canonical_maps is processed before $canonical_maps.

Example:

recipient_canonical_maps = hash:/usr/local/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 821.

relay_destination_concurrency_limit (default: $default_destination_concurrency_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 version 2.0 and later.

relay_destination_recipient_limit (default: $default_destination_recipient_limit)
The maximal number of recipients per delivery 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.

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 version 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 parent_domain_matches_subdomains parameter. For details about how the relay_domains value is used, see the description of the permit_auth_destination and reject_unauth_destination SMTP recipient restrictions.

Domains that match $relay_domains are delivered with the $relay_transport mail delivery transport. The SMTP server validates recipient addresses with $relay_recipient_maps and rejects non-existent recipients. 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 permit_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.

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 821.

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 do not have a valid recipient list. 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:/usr/local/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 information for domains that match the $relay_domains parameter value. This information can be overruled with the transport(5) table.

Specify a string of the form transport:nexthop, where transport is the name of a mail delivery transport defined in master.cf. The :nexthop part is optional. For more details see the transport(5) manual page.

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 default host to send non-local mail to when no entry is matched in the optional transport(5) table. When no relayhost is given, mail is routed directly to the destination.

On an intranet, specify the organizational domain name. If your internal 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 [hostname] turns off MX lookups.

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

Examples:

relayhost = $mydomain
relayhost = [gateway.my.domain]
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 documented in relocated(5).

If you use this feature, run "postmap /usr/local/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:/usr/local/etc/postfix/relocated
relocated_maps = hash:/usr/local/etc/postfix/relocated

require_home_directory (default: no)
Whether or not a local(8) recipient's home directory must exist 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 (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 incorrect.

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 version 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 rewrite into a form that ends in the "@" null domain.

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: /usr/local/etc/postfix)
The name of the directory with example Postfix configuration files.

sender_based_routing (default: no)
This parameter should not be used.

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 /usr/local/etc/postfix/sender_bcc".

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

Example:

sender_bcc_maps = hash:/usr/local/etc/postfix/sender_bcc

sender_canonical_maps (default: empty)
Optional address mapping lookup tables for envelope and header sender addresses. The table format and lookups are documented in canonical(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 RECIPIENT address "user@ugly.domain".

Note: $sender_canonical_maps is processed before $canonical_maps.

Example:

sender_canonical_maps = hash:/usr/local/etc/postfix/sender_canonical

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 "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 status 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 SMTP client should bind to when making a 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 example:

  /usr/local/etc/postfix/master.cf:
        smtp ... smtp -o smtp_bind_address=11.22.33.44

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 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_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 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_concurrency_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_recipient_limit)
The maximal number of recipients per delivery 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.

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

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:

  /usr/local/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 when the SMTP client uses to look up a host's IP address. This parameter is ignored when DNS lookups are disabled.

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_mx_address_limit (default: 0)
The maximal number of MX (mail exchanger) IP addresses that can result from mail exchanger lookups, or zero (no limit).

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 IP addresses that fail to complete the SMTP initial handshake.

This feature is available in Postfix 2.1 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 sending large messages over slow network connections.

smtp_pix_workaround_threshold_time (default: 500s)
How long a message must be queued before the PIX firewall "<CR><LF>.<CR><LF>" bug workaround is 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_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 821. This includes putting quotes around an address localpart that ends in ".".

The default is to comply with RFC 821. If you have to send mail to a broken SMTP server, configure a special SMTP client in master.cf:

    /usr/local/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_rset_timeout (default: 120s)
The SMTP client time limit for sending the RSET command, and for receiving the server response.

This feature is available in Postfix 2.1 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_password_maps (default: empty)
Optional SMTP client lookup tables with one username:password entry per remote hostname or domain. If a remote host or domain has no username:password entry, 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 /usr/local/etc/postfix.

smtp_sasl_security_options (default: noplaintext, noanonymous)
What authentication mechanisms the Postfix SMTP client is allowed to use. 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.

mutual_auth
    Only allow methods that provide mutual authentication (not available with SASL version 1).

Example:

smtp_sasl_security_options = noplaintext

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_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 immediately.

This feature is available in Postfix version 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_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 command 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 2.1. The default value is backwards compatible with Postfix 2.0.

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.

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. Typical 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.

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.

smtpd_authorized_xforward_hosts (default: empty)
What SMTP clients are allowed to use the XFORWARD feature. This command 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.

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.

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, Postfix 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 SMTP client is allowed to make to the SMTP service. By default, the limit is set it 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 not part of the stable Postfix 2.1 release.

smtpd_client_connection_limit_exceptions (default: $mynetworks)
Clients that are excluded from connection count or connection rate restrictions.

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).

This feature is not part of the stable Postfix 2.1 release.

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, and defaults to one minute.

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 not part of the stable Postfix 2.1 release.

Example:

smtpd_client_connection_rate_limit = 1000

smtpd_client_restrictions (default: empty)
Optional SMTP server access restrictions in the context of a client SMTP connection request.

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 restriction that matches wins.

The following restrictions are specific to client hostname or client network address information.

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.

permit_mynetworks
    Permit the request when the client IP address matches any network listed in $mynetworks.

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 reversed client network address 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
    Reject the request when the client IP address has no PTR (address to name) record in the DNS, or when the PTR record does not have a matching A (name to address) record.
    The unknown_client_reject_code parameter specifies the response code for rejected requests (default: 450). The reply is always 450 in case the hostname lookup failed due to a temporary problem.

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 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 Postfix 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. Although this usage is technically allowed, it seems to have no legitimate application.
    The multi_recipient_bounce_reject_code parameter specifies the response code for rejected requests (default: 550). This feature is available in Postfix 2.1 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 commands ahead of time without knowing that Postfix actually supports SMTP command pipelining. This stops mail from bulk mail software that improperly uses SMTP command pipelining in order to speed up deliveries.

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 to rejected requests (default: 554).

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_restrictions, 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

smtpd_data_restrictions (default: empty)
Optional access restrictions that the Postfix SMTP server applies in the context of the SMTP DATA command.

This feature is available in Postfix 2.0 and later.

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 restriction that matches wins.

The following restrictions are valid in this context:

•   Generic restrictions that can be used in any SMTP command context, 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_reject (default: yes)
Wait until the RCPT TO command before evaluating $smtpd_client_restrictions, $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_error_sleep_time (default: 1s)
With Postfix 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 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.

The Postfix ETRN implementation accepts only destinations that are eligible for the Postfix "fast flush" service. See the ETRN_README file for details.

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 restriction that matches wins.

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 context, 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_hard_error_limit (default: 20)
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.

smtpd_helo_required (default: no)
Require that a remote SMTP client introduces itself at the beginning of an SMTP session with the HELO or EHLO command.

Example:

smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
Optional restrictions that the Postfix SMTP server applies in the context of the SMTP HELO command.

The default is to permit everything.

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 restriction that matches wins.

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_hostname
    Reject the request when the HELO or EHLO hostname syntax is invalid.
    The invalid_hostname_reject_code specifies the response code to rejected requests (default: 501).

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 to rejected requests (default: 504).

reject_unknown_hostname
    Reject the request when the HELO or EHLO hostname has no DNS A or MX record.
    The unknown_hostname_reject_code specifies the response code to rejected requests (default: 450).

Other restrictions that are valid in this context:

•   Generic restrictions that can be used in any SMTP command context, 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_hostname
smtpd_helo_restrictions = permit_mynetworks, reject_unknown_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: 100)
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.

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_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 delegated 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. 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.

This feature is available in Postfix 2.1 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_destination)
The access restrictions that the Postfix SMTP server applies in the context of the RCPT TO command.

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@elsewhere@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

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 restriction that matches wins.

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 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_recipient_ns_access type:table
    Search the specified access(5) database for the DNS servers for the RCPT TO 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.

permit_auth_destination
    Permit the request when one of the following is true:

•   Postfix is mail forwarder: the resolved RCPT TO address 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 address matches $mydestination, $inet_interfaces, $proxy_interfaces, $virtual_alias_domains, or $virtual_mailbox_domains, and the address contains no sender-specified routing (user@elsewhere@domain).

permit_mx_backup
    Permit the request when the local mail system is MX host for the RCPT TO address. This includes the case that the local mail system is the final destination. However, the SMTP server will not forward mail with addresses that have sender-specified routing information (example: user@elsewhere@domain). Use the optional permit_mx_backup_networks parameter to require that the primary MX hosts match a list of network blocks.
    NOTE: prior to Postfix version 2.0, use of permit_mx_backup is not recommended; mail may be rejected in case of a temporary DNS lookup problem.

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 to 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 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_unauth_destination
    Reject the request unless one of the following is true:

•   Postfix is mail forwarder: the resolved RCPT TO address 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 address matches $mydestination, $inet_interfaces, $proxy_interfaces, $virtual_alias_domains, or $virtual_mailbox_domains, and contains 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 the RCPT TO address has no DNS A or MX record and Postfix is not final destination for the recipient address.
    The unknown_address_reject_code parameter specifies the response code for rejected requests (default: 450). The response is always 450 in case of a temporary DNS error.

reject_unlisted_recipient (Postfix 2.0 name: check_recipient_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 reachable. Address verification information is managed by the verify(8) server; see the ADDRESS_VERIFICATION_README file for details.
    The unverified_recipient_reject_code parameter specifies the response when an address is known to bounce (default: 450, change into 550 when you are confident that it is safe to do so). Postfix replies with 450 when an address probe failed due to a temporary problem. 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 context, 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.

•   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 $virtual_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 restriction is specified. This can slow down an explosion of forged mail from worms or viruses.

•   The sender 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 sender domain matches $virtual_alias_domains but the recipient is not listed in $virtual_alias_maps.

•   The sender domain matches $virtual_mailbox_domains but the recipient is not listed in $virtual_mailbox_maps, and $virtual_mailbox_maps is not null.

•   The sender 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_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 used 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 later.

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_exceptions_networks (default: empty)
What SMTP clients Postfix 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, $mynetworks 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.

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 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_security_options (default: noanonymous)
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.

mutual_auth
    Only allow methods that provide mutual authentication (not available with 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_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_interfaces 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 context of the MAIL FROM command.

The default is to permit everything.

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 restriction that matches wins.

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 to 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 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_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 unauthenticated clients only. This feature is available in Postfix version 2.1 and later.

reject_unknown_sender_domain
    Reject the request when the MAIL FROM address has no DNS A or MX record and Postfix is not final destination for the sender address.
    The unknown_address_reject_code parameter specifies the response code for rejected requests (default: 450). The response is always 450 in case of a temporary DNS error.

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 reachable. Address verification information is managed by the verify(8) server; see the ADDRESS_VERIFICATION_README file for details.
    The unverified_sender_reject_code parameter specifies the response when an address is known to bounce (default: 450, change into 550 when you are confident that it is safe to do so). Postfix replies with 450 when an address probe failed due to a temporary problem. 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 context, 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_recipient_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:/usr/local/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_timeout (default: 300s)
The time limit for sending a Postfix SMTP server response and for receiving a remote SMTP client request.

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).

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 prevents 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).

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_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 software.

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 "mailbox_delivery_lock = dotlock".

swap_bangpath (default: yes)
Enable the rewriting of "site!user" into "user@site". This is necessary if your machine is connected to UUCP networks. It is enabled by default.

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: postfix)
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.

trace_service_name (default: trace)
The name of the trace(8) service. This service maintains a record of mail deliveries and produces a mail delivery report when verbose delivery is requested with "sendmail -v".

This feature is available in Postfix 2.1 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 feature with local files, run "postmap /usr/local/etc/postfix/transport" after making a change.

Examples:

transport_maps = dbm:/usr/local/etc/postfix/transport
transport_maps = hash:/usr/local/etc/postfix/transport

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).

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 message contains no To: or Cc: message header.

unknown_address_reject_code (default: 450)
The numerical Postfix SMTP server response code when a sender or recipient address is rejected by the reject_unknown_sender_domain or reject_unknown_recipient_domain restriction.

Do not change this unless you have a complete understanding of RFC 821.

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 restriction. The SMTP server always replies with 450 when the mapping failed due to a temporary error condition.

Do not change this unless you have a complete understanding of RFC 821.

unknown_hostname_reject_code (default: 450)
The numerical Postfix SMTP server response code when the hostname specified with the HELO or EHLO command is rejected by the reject_unknown_hostname restriction.

Do not change this unless you have a complete understanding of RFC 821.

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 $virtual_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 $virtual_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_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 821.

This feature is available in Postfix 2.1 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 821.

This feature is available in Postfix 2.1 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)
Optional list of names 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 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 frequently (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 whitespace.

See also the VIRTUAL_README and ADDRESS_CLASS_README documents for further 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 documented in virtual(5).

This feature is available in Postfix 2.0 and later. The default value is backwards compatible with Postfix 1.1.

If you use this feature with indexed files, run "postmap /usr/local/etc/postfix/virtual" after changing the file.

Examples:

virtual_alias_maps = dbm:/usr/local/etc/postfix/virtual
virtual_alias_maps = hash:/usr/local/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_concurrency_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_recipient_limit)
The maximal number of recipients per delivery 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.

Setting this parameter to a value of 1 changes the meaning of virtual_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 does not allow table lookup through the proxymap(8) service, because that would open a security hole.

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)
The list of domains that are 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 configuration parameter.

This feature is available in Postfix 2.0 and later. The default value is backwards compatible with Postfix 1.1.

virtual_mailbox_limit (default: 51200000)
The maximal size in bytes of an individual 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-recipient 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_mailbox_base is unconditionally prepended to this path.

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 disallows table lookup through the proxymap(8) server, 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 2.0 and later, this is replaced by separate controls: virtual_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 for domains that match the $virtual_mailbox_domains parameter value. This information can be overruled with the transport(5) table.

Specify a string of the form transport:nexthop, where transport is the name of a mail delivery transport defined in master.cf. The :nexthop part is optional. For more details see the transport(5) manual page.

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) delivery 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.

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 does not allow table lookup through the proxymap(8) service, because that would open a security hole.

SEE ALSO
postconf(1) postfix configuration maintenance

LICENSE
The Secure Mailer license must be distributed with this software.

AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA