man local (8): Postfix local mail delivery

SYNOPSIS

local [generic Postfix daemon options]

DESCRIPTION

The local(8) daemon processes delivery requests from the Postfix queue manager to deliver mail to local recipients. Each delivery request specifies a queue file, a sender address, a domain or host to deliver to, and one or more recipients. This program expects to be run from the master(8) process manager.

The local(8) daemon updates queue files and marks recipients as finished, or it informs the queue manager that delivery should be tried again at a later time. Delivery status reports are sent to the bounce(8), defer(8) or trace(8) daemon as appropriate.

CASE FOLDING

All delivery decisions are made using the bare recipient name (i.e. the address localpart), folded to lower case. See also under ADDRESS EXTENSION below for a few exceptions.

SYSTEM-WIDE AND USER-LEVEL ALIASING

The system administrator can set up one or more system-wide sendmail-style alias databases. Users can have sendmail-style ~/.forward files. Mail for name is delivered to the alias name, to destinations in ~name/.forward, to the mailbox owned by the user name, or it is sent back as undeliverable.

The system administrator can specify a comma/space separated list of ~/.forward like files through the forward_path configuration parameter. Upon delivery, the local delivery agent tries each pathname in the list until a file is found.

Delivery via ~/.forward files is done with the privileges of the recipient. Thus, ~/.forward like files must be readable by the recipient, and their parent directory needs to have "execute" permission for the recipient.

The forward_path parameter is subject to interpolation of $user (recipient username), $home (recipient home directory), $shell (recipient shell), $recipient (complete recipient address), $extension (recipient address extension), $domain (recipient domain), $local (entire recipient address localpart) and $recipient_delimiter. The forms ${name?value} and ${name:value} expand conditionally to value when $name is (is not) defined. Characters that may have special meaning to the shell or file system are replaced by underscores. The list of acceptable characters is specified with the forward_expansion_filter configuration parameter.

An alias or ~/.forward file may list any combination of external commands, destination file names, :include: directives, or mail addresses. See aliases(5) for a precise description. Each line in a user's .forward file has the same syntax as the right-hand part of an alias.

When an address is found in its own alias expansion, delivery is made to the user instead. When a user is listed in the user's own ~/.forward file, delivery is made to the user's mailbox instead. An empty ~/.forward file means do not forward mail.

In order to prevent the mail system from using up unreasonable amounts of memory, input records read from :include: or from ~/.forward files are broken up into chunks of length line_length_limit.

While expanding aliases, ~/.forward files, and so on, the program attempts to avoid duplicate deliveries. The duplicate_filter_limit configuration parameter limits the number of remembered recipients.

MAIL FORWARDING

For the sake of reliability, forwarded mail is re-submitted as a new message, so that each recipient has a separate on-file delivery status record.

In order to stop mail forwarding loops early, the software adds an optional Delivered-To: header with the final envelope recipient address. If mail arrives for a recipient that is already listed in a Delivered-To: header, the message is bounced.

MAILBOX DELIVERY

The default per-user mailbox is a file in the UNIX mail spool directory (/var/mail/user or /var/spool/mail/user); the location can be specified with the mail_spool_directory configuration parameter. Specify a name ending in / for qmail-compatible maildir delivery.

Alternatively, the per-user mailbox can be a file in the user's home directory with a name specified via the home_mailbox configuration parameter. Specify a relative path name. Specify a name ending in / for qmail-compatible maildir delivery.

Mailbox delivery can be delegated to an external command specified with the mailbox_command_maps and mailbox_command configuration parameters. The command executes with the privileges of the recipient user (exceptions: secondary groups are not enabled; in case of delivery as root, the command executes with the privileges of default_privs).

Mailbox delivery can be delegated to alternative message transports specified in the master.cf file. The mailbox_transport_maps and mailbox_transport configuration parameters specify an optional message transport that is to be used for all local recipients, regardless of whether they are found in the UNIX passwd database. The fallback_transport_maps and fallback_transport parameters specify an optional message transport for recipients that are not found in the aliases(5) or UNIX passwd database.

In the case of UNIX-style mailbox delivery, the local(8) daemon prepends a "From sender time_stamp" envelope header to each message, prepends an X-Original-To: header with the recipient address as given to Postfix, prepends an optional Delivered-To: header with the final envelope recipient address, prepends a Return-Path: header with the envelope sender address, prepends a > character to lines beginning with "From ", and appends an empty line. The mailbox is locked for exclusive access while delivery is in progress. In case of problems, an attempt is made to truncate the mailbox to its original length.

In the case of maildir delivery, the local daemon prepends an optional Delivered-To: header with the final envelope recipient address, prepends an X-Original-To: header with the recipient address as given to Postfix, and prepends a Return-Path: header with the envelope sender address.

EXTERNAL COMMAND DELIVERY

The allow_mail_to_commands configuration parameter restricts delivery to external commands. The default setting (alias, forward) forbids command destinations in :include: files.

Optionally, the process working directory is changed to the path specified with command_execution_directory (Postfix 2.2 and later). Failure to change directory causes mail to be deferred.

The command_execution_directory parameter value is subject to interpolation of $user (recipient username), $home (recipient home directory), $shell (recipient shell), $recipient (complete recipient address), $extension (recipient address extension), $domain (recipient domain), $local (entire recipient address localpart) and $recipient_delimiter. The forms ${name?value} and ${name:value} expand conditionally to value when $name is (is not) defined. Characters that may have special meaning to the shell or file system are replaced by underscores. The list of acceptable characters is specified with the execution_directory_expansion_filter configuration parameter.

The command is executed directly where possible. Assistance by the shell (/bin/sh on UNIX systems) is used only when the command contains shell magic characters, or when the command invokes a shell built-in command.

A limited amount of command output (standard output and standard error) is captured for inclusion with non-delivery status reports. A command is forcibly terminated if it does not complete within command_time_limit seconds. Command exit status codes are expected to follow the conventions defined in <sysexits.h>. Exit status 0 means normal successful completion.

Postfix version 2.3 and later support RFC 3463-style enhanced status codes. If a command terminates with a non-zero exit status, and the command output begins with an enhanced status code, this status code takes precedence over the non-zero exit status.

A limited amount of message context is exported via environment variables. Characters that may have special meaning to the shell are replaced by underscores. The list of acceptable characters is specified with the command_expansion_filter configuration parameter.

SHELL: The recipient user's login shell.
HOME: The recipient user's home directory.
USER: The bare recipient name.
EXTENSION: The optional recipient address extension.
DOMAIN: The recipient address domain part.
LOGNAME: The bare recipient name.
LOCAL: The entire recipient address localpart (text to the left of the rightmost @ character).
ORIGINAL_RECIPIENT: The entire recipient address, before any address rewriting or aliasing (Postfix 2.5 and later).
RECIPIENT: The entire recipient address.
SENDER: The entire sender address.

Additional remote client information is made available via the following environment variables:

CLIENT_ADDRESS: Remote client network address. Available as of Postfix 2.2.
CLIENT_HELO: Remote client EHLO command parameter. Available as of Postfix 2.2.
CLIENT_HOSTNAME: Remote client hostname. Available as of Postfix 2.2.
CLIENT_PROTOCOL: Remote client protocol. Available as of Postfix 2.2.
SASL_METHOD: SASL authentication method specified in the remote client AUTH command. Available as of Postfix 2.2.
SASL_SENDER: SASL sender address specified in the remote client MAIL FROM command. Available as of Postfix 2.2.
SASL_USERNAME: SASL username specified in the remote client AUTH command. Available as of Postfix 2.2.

The PATH environment variable is always reset to a system-dependent default path, and environment variables whose names are blessed by the export_environment configuration parameter are exported unchanged.

The current working directory is the mail queue directory.

The local(8) daemon prepends a "From sender time_stamp" envelope header to each message, prepends an X-Original-To: header with the recipient address as given to Postfix, prepends an optional Delivered-To: header with the final recipient envelope address, prepends a Return-Path: header with the sender envelope address, and appends no empty line.

EXTERNAL FILE DELIVERY

The delivery format depends on the destination filename syntax. The default is to use UNIX-style mailbox format. Specify a name ending in / for qmail-compatible maildir delivery.

The allow_mail_to_files configuration parameter restricts delivery to external files. The default setting (alias, forward) forbids file destinations in :include: files.

In the case of UNIX-style mailbox delivery, the local(8) daemon prepends a "From sender time_stamp" envelope header to each message, prepends an X-Original-To: header with the recipient address as given to Postfix, prepends an optional Delivered-To: header with the final recipient envelope address, prepends a > character to lines beginning with "From ", and appends an empty line. The envelope sender address is available in the Return-Path: header. When the destination is a regular file, it is locked for exclusive access while delivery is in progress. In case of problems, an attempt is made to truncate a regular file to its original length.

In the case of maildir delivery, the local daemon prepends an optional Delivered-To: header with the final envelope recipient address, and prepends an X-Original-To: header with the recipient address as given to Postfix. The envelope sender address is available in the Return-Path: header.

ADDRESS EXTENSION

The optional recipient_delimiter configuration parameter specifies how to separate address extensions from local recipient names.

For example, with "recipient_delimiter = +", mail for name+foo is delivered to the alias name+foo or to the alias name, to the destinations listed in ~name/.forward+foo or in ~name/.forward, to the mailbox owned by the user name, or it is sent back as undeliverable.

DELIVERY RIGHTS

Deliveries to external files and external commands are made with the rights of the receiving user on whose behalf the delivery is made. In the absence of a user context, the local(8) daemon uses the owner rights of the :include: file or alias database. When those files are owned by the superuser, delivery is made with the rights specified with the default_privs configuration parameter.

STANDARDS

RFC 822 (ARPA Internet Text Messages)
RFC 3463 (Enhanced status codes)

DIAGNOSTICS

Problems and transactions are logged to syslogd(8). Corrupted message files are marked so that the queue manager can move them to the corrupt queue afterwards.

Depending on the setting of the notify_classes parameter, the postmaster is notified of bounces and of other trouble.

SECURITY

The local(8) delivery agent needs a dual personality 1) to access the private Postfix queue and IPC mechanisms, 2) to impersonate the recipient and deliver to recipient-specified files or commands. It is therefore security sensitive.

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

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

BUGS

For security reasons, the message delivery status of external commands or of external files is never checkpointed to file. As a result, the program may occasionally deliver more than once to a command or external file. Better safe than sorry.

Mutually-recursive aliases or ~/.forward files are not detected early. The resulting mail forwarding loop is broken by the use of the Delivered-To: message header.

CONFIGURATION PARAMETERS

Changes to main.cf are picked up automatically, as local(8) processes run for only a limited amount of time. Use the command "postfix reload" to speed up a change.

The text below provides only a parameter summary. See postconf(5) for more details including examples.

COMPATIBILITY CONTROLS

biff (yes): Whether or not to use the local biff service.
expand_owner_alias (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.
owner_request_special (yes): Give special treatment to owner-listname and listname-request address localparts: don't split such addresses when the recipient_delimiter is set to "-".
sun_mailtool_compatibility (no): Obsolete SUN mailtool compatibility feature.

Available in Postfix version 2.3 and later:

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

Available in Postfix version 2.5.3 and later:

strict_mailbox_ownership (yes): Defer delivery when a mailbox file is not owned by its recipient.
reset_owner_alias (no): Reset the local(8) delivery agent's idea of the owner-alias attribute, when delivering mail to a child alias that does not have its own owner alias.

Available in Postfix version 3.0 and later:

local_delivery_status_filter ($default_delivery_status_filter): Optional filter for the local(8) delivery agent to change the status code or explanatory text of successful or unsuccessful deliveries.

DELIVERY METHOD CONTROLS

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

alias_maps (see 'postconf -d' output): The alias databases that are used for local(8) delivery.
forward_path (see 'postconf -d' output): The local(8) delivery agent search list for finding a .forward file with user-specified delivery methods.
mailbox_transport_maps (empty): Optional lookup tables with per-recipient message delivery transports to use for local(8) mailbox delivery, whether or not the recipients are found in the UNIX passwd database.
mailbox_transport (empty): Optional message delivery transport that the local(8) delivery agent should use for mailbox delivery to all local recipients, whether or not they are found in the UNIX passwd database.
mailbox_command_maps (empty): Optional lookup tables with per-recipient external commands to use for local(8) mailbox delivery.
mailbox_command (empty): Optional external command that the local(8) delivery agent should use for mailbox delivery.
home_mailbox (empty): Optional pathname of a mailbox file relative to a local(8) user's home directory.
mail_spool_directory (see 'postconf -d' output): The directory where local(8) UNIX-style mailboxes are kept.
fallback_transport_maps (empty): Optional lookup tables with per-recipient message delivery transports for recipients that the local(8) delivery agent could not find in the aliases(5) or UNIX password database.
fallback_transport (empty): Optional message delivery transport that the local(8) delivery agent should use for names that are not found in the aliases(5) or UNIX password database.
luser_relay (empty): Optional catch-all destination for unknown local(8) recipients.

Available in Postfix version 2.2 and later:

command_execution_directory (empty): The local(8) delivery agent working directory for delivery to external command.

MAILBOX LOCKING CONTROLS

deliver_lock_attempts (20): The maximal number of attempts to acquire an exclusive lock on a mailbox file or bounce(8) logfile.
deliver_lock_delay (1s): The time between attempts to acquire an exclusive lock on a mailbox file or bounce(8) logfile.
stale_lock_time (500s): The time after which a stale exclusive mailbox lockfile is removed.
mailbox_delivery_lock (see 'postconf -d' output): How to lock a UNIX-style local(8) mailbox before attempting delivery.

RESOURCE AND RATE CONTROLS

command_time_limit (1000s): Time limit for delivery to external commands.
duplicate_filter_limit (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.
local_destination_concurrency_limit (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").
local_destination_recipient_limit (1): The maximal number of recipients per message delivery via the local mail delivery transport.
mailbox_size_limit (51200000): The maximal size of any local(8) individual mailbox or maildir file, or zero (no limit).

SECURITY CONTROLS

allow_mail_to_commands (alias, forward): Restrict local(8) mail delivery to external commands.
allow_mail_to_files (alias, forward): Restrict local(8) mail delivery to external files.
command_expansion_filter (see 'postconf -d' output): Restrict the characters that the local(8) delivery agent allows in $name expansions of $mailbox_command and $command_execution_directory.
default_privs (nobody): The default rights used by the local(8) delivery agent for delivery to external file or command.
forward_expansion_filter (see 'postconf -d' output): Restrict the characters that the local(8) delivery agent allows in $name expansions of $forward_path.