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PIPE(8postfix) PIPE(8postfix)

NAME
pipe - Postfix delivery to external command

SYNOPSIS
pipe [generic Postfix daemon options] command_attributes...

DESCRIPTION
The pipe(8) daemon processes requests from the Postfix queue manager to deliver messages to
external commands. This program expects to be run from the master(8) process manager.

Message attributes such as sender address, recipient address and next-hop host name can be
specified as command-line macros that are expanded before the external command is executed.

The pipe(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.

SINGLE-RECIPIENT DELIVERY
Some destinations cannot handle more than one recipient per delivery request. Examples are
pagers or fax machines. In addition, multi-recipient delivery is undesirable when prepending
a Delivered-to: or X-Original-To: message header.

To prevent Postfix from sending multiple recipients per delivery request, specify

transport_destination_recipient_limit = 1

in the Postfix main.cf file, where transport is the name in the first column of the Postfix
master.cf entry for the pipe-based delivery transport.

COMMAND ATTRIBUTE SYNTAX
The external command attributes are given in the master.cf file at the end of a service defi‐
nition. The syntax is as follows:

chroot=pathname (optional)
Change the process root directory and working directory to the named directory. This
happens before switching to the privileges specified with the user attribute, and be‐
fore executing the optional directory=pathname directive. Delivery is deferred in case
of failure.

This feature is available as of Postfix 2.3.

directory=pathname (optional)
Change to the named directory before executing the external command. The directory
must be accessible for the user specified with the user attribute (see below). The
default working directory is $queue_directory. Delivery is deferred in case of fail‐
ure.

This feature is available as of Postfix 2.2.

eol=string (optional, default: \n)
The output record delimiter. Typically one would use either \r\n or \n. The usual
C-style backslash escape sequences are recognized: \a \b \f \n \r \t \v \ddd (up to
three octal digits) and \\.

flags=BDFORXhqu.> (optional)
Optional message processing flags. By default, a message is copied unchanged.

B Append a blank line at the end of each message. This is required by some mail
user agents that recognize "From " lines only when preceded by a blank line.

D Prepend a "Delivered-To: recipient" message header with the envelope recipient
address. Note: for this to work, the transport_destination_recipient_limit must
be 1 (see SINGLE-RECIPIENT DELIVERY above for details).

The D flag also enforces loop detection (Postfix 2.5 and later): if a message
already contains a Delivered-To: header with the same recipient address, then
the message is returned as undeliverable. The address comparison is case insen‐
sitive.

This feature is available as of Postfix 2.0.

F Prepend a "From sender time_stamp" envelope header to the message content.
This is expected by, for example, UUCP software.

O Prepend an "X-Original-To: recipient" message header with the recipient address
as given to Postfix. Note: for this to work, the transport_destination_recipi‐‐
ent_limit must be 1 (see SINGLE-RECIPIENT DELIVERY above for details).

This feature is available as of Postfix 2.0.

R Prepend a Return-Path: message header with the envelope sender address.

X Indicate that the external command performs final delivery. This flag affects
the status reported in "success" DSN (delivery status notification) messages,
and changes it from "relayed" into "delivered".

This feature is available as of Postfix 2.5.

h Fold the command-line $original_recipient and $recipient address domain part
(text to the right of the right-most @ character) to lower case; fold the en‐
tire command-line $domain and $nexthop host or domain information to lower
case. This is recommended for delivery via UUCP.

q Quote white space and other special characters in the command-line $sender,
$original_recipient and $recipient address localparts (text to the left of the
right-most @ character), according to an 8-bit transparent version of RFC 822.
This is recommended for delivery via UUCP or BSMTP.

The result is compatible with the address parsing of command-line recipients by
the Postfix sendmail(1) mail submission command.

The q flag affects only entire addresses, not the partial address information
from the $user, $extension or $mailbox command-line macros.

u Fold the command-line $original_recipient and $recipient address localpart
(text to the left of the right-most @ character) to lower case. This is recom‐
mended for delivery via UUCP.

. Prepend "." to lines starting with ".". This is needed by, for example, BSMTP
software.

> Prepend ">" to lines starting with "From ". This is expected by, for example,
UUCP software.

null_sender=replacement (default: MAILER-DAEMON)
Replace the null sender address (typically used for delivery status notifications)
with the specified text when expanding the $sender command-line macro, and when gener‐
ating a From_ or Return-Path: message header.

If the null sender replacement text is a non-empty string then it is affected by the q
flag for address quoting in command-line arguments.

The null sender replacement text may be empty; this form is recommended for content
filters that feed mail back into Postfix. The empty sender address is not affected by
the q flag for address quoting in command-line arguments.

Caution: a null sender address is easily mis-parsed by naive software. For example,
when the pipe(8) daemon executes a command such as:

Wrong: command -f$sender -- $recipient

the command will mis-parse the -f option value when the sender address is a null
string. For correct parsing, specify $sender as an argument by itself:

Right: command -f $sender -- $recipient

This feature is available as of Postfix 2.3.

size=size_limit (optional)
Don't deliver messages that exceed this size limit (in bytes); return them to the
sender instead.

user=username (required)

user=username:groupname
Execute the external command with the user ID and group ID of the specified username.
The software refuses to execute commands with root privileges, or with the privileges
of the mail system owner. If groupname is specified, the corresponding group ID is
used instead of the group ID of username.

argv=command... (required)
The command to be executed. This must be specified as the last command attribute. The
command is executed directly, i.e. without interpretation of shell meta characters by
a shell command interpreter.

Specify "{" and "}" around command arguments that contain whitespace (Postfix 3.0 and
later). Whitespace after the opening "{" and before the closing "}" is ignored.

In the command argument vector, the following macros are recognized and replaced with
corresponding information from the Postfix queue manager delivery request.

In addition to the form ${name}, the forms $name and the deprecated form $(name) are
also recognized. Specify $$ where a single $ is wanted.

${client_address}
This macro expands to the remote client network address.

This feature is available as of Postfix 2.2.

${client_helo}
This macro expands to the remote client HELO command parameter.

This feature is available as of Postfix 2.2.

${client_hostname}
This macro expands to the remote client hostname.

This feature is available as of Postfix 2.2.

${client_port}
This macro expands to the remote client TCP port number.

This feature is available as of Postfix 2.5.

${client_protocol}
This macro expands to the remote client protocol.

This feature is available as of Postfix 2.2.

${domain}
This macro expands to the domain portion of the recipient address. For exam‐
ple, with an address user+foo@domain the domain is domain.

This information is modified by the h flag for case folding.

This feature is available as of Postfix 2.5.

${extension}
This macro expands to the extension part of a recipient address. For example,
with an address user+foo@domain the extension is foo.

A command-line argument that contains ${extension} expands into as many com‐
mand-line arguments as there are recipients.

This information is modified by the u flag for case folding.

${mailbox}
This macro expands to the complete local part of a recipient address. For ex‐
ample, with an address user+foo@domain the mailbox is user+foo.

A command-line argument that contains ${mailbox} expands to as many com‐
mand-line arguments as there are recipients.

This information is modified by the u flag for case folding.

${nexthop}
This macro expands to the next-hop hostname.

This information is modified by the h flag for case folding.

${original_recipient}
This macro expands to the complete recipient address before any address rewrit‐
ing or aliasing.

A command-line argument that contains ${original_recipient} expands to as many
command-line arguments as there are recipients.

This information is modified by the hqu flags for quoting and case folding.

This feature is available as of Postfix 2.5.

${queue_id}
This macro expands to the queue id.

This feature is available as of Postfix 2.11.

${recipient}
This macro expands to the complete recipient address.

A command-line argument that contains ${recipient} expands to as many com‐
mand-line arguments as there are recipients.

This information is modified by the hqu flags for quoting and case folding.

${sasl_method}
This macro expands to the name of the SASL authentication mechanism in the AUTH
command when the Postfix SMTP server received the message.

This feature is available as of Postfix 2.2.

${sasl_sender}
This macro expands to the SASL sender name (i.e. the original submitter as per
RFC 4954) in the MAIL FROM command when the Postfix SMTP server received the
message.

This feature is available as of Postfix 2.2.

${sasl_username}
This macro expands to the SASL user name in the AUTH command when the Postfix
SMTP server received the message.

This feature is available as of Postfix 2.2.

${sender}
This macro expands to the envelope sender address. By default, the null sender
address expands to MAILER-DAEMON; this can be changed with the null_sender at‐
tribute, as described above.

This information is modified by the q flag for quoting.

${size}
This macro expands to Postfix's idea of the message size, which is an approxi‐
mation of the size of the message as delivered.

${user}
This macro expands to the username part of a recipient address. For example,
with an address user+foo@domain the username part is user.

A command-line argument that contains ${user} expands into as many command-line
arguments as there are recipients.

This information is modified by the u flag for case folding.

STANDARDS
RFC 3463 (Enhanced status codes)

DIAGNOSTICS
Command exit status codes are expected to follow the conventions defined in <sysexits.h>.
Exit status 0 means normal successful completion.

In the case of a non-zero exit status, a limited amount of command output is logged, and re‐
ported in a delivery status notification. When the output begins with a 4.X.X or 5.X.X en‐
hanced status code, the status code takes precedence over the non-zero exit status (Postfix
version 2.3 and later).

After successful delivery (zero exit status) a limited amount of command output is logged,
and reported in "success" delivery status notifications (Postfix 3.0 and later). This com‐
mand output is not examined for the presence of an enhanced status code.

Problems and transactions are logged to syslogd(8) or postlogd(8). Corrupted message files
are marked so that the queue manager can move them to the corrupt queue for further inspec‐
tion.

SECURITY
This program needs a dual personality 1) to access the private Postfix queue and IPC mecha‐
nisms, and 2) to execute external commands as the specified user. It is therefore security
sensitive.

CONFIGURATION PARAMETERS
Changes to main.cf are picked up automatically as pipe(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.

RESOURCE AND RATE CONTROLS
In the text below, transport is the first field in a master.cf entry.

transport_time_limit ($command_time_limit)
A transport-specific override for the command_time_limit parameter value, where trans‐
port is the master.cf name of the message delivery transport.

Implemented in the qmgr(8) daemon:

transport_destination_concurrency_limit ($default_destination_concurrency_limit)
A transport-specific override for the default_destination_concurrency_limit parameter
value, where transport is the master.cf name of the message delivery transport.

transport_destination_recipient_limit ($default_destination_recipient_limit)
A transport-specific override for the default_destination_recipient_limit parameter
value, where transport is the master.cf name of the message delivery transport.

MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf configuration files.

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

delay_logging_resolution_limit (2)
The maximal number of digits after the decimal point when logging sub-second delay
values.

export_environment (see 'postconf -d' output)
The list of environment variables that a Postfix process will export to non-Postfix
processes.

ipc_timeout (3600s)
The time limit for sending or receiving information over an internal communication
channel.

mail_owner (postfix)
The UNIX system account that owns the Postfix queue and most Postfix daemon processes.

max_idle (100s)
The maximum amount of time that an idle Postfix daemon process waits for an incoming
connection before terminating voluntarily.

max_use (100)
The maximal number of incoming connections that a Postfix daemon process will service
before terminating voluntarily.

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

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

queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue directory.

recipient_delimiter (empty)
The set of characters that can separate a user name from its extension (example:
user+foo), or a .forward file name from its extension (example: .forward+foo).

syslog_facility (mail)
The syslog facility of Postfix logging.

syslog_name (see 'postconf -d' output)
A prefix that is prepended to the process name in syslog records, so that, for exam‐
ple, "smtpd" becomes "prefix/smtpd".

Available in Postfix version 3.0 and later:

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

Available in Postfix version 3.3 and later:

enable_original_recipient (yes)
Enable support for the original recipient address after an address is rewritten to a
different address (for example with aliasing or with canonical mapping).

service_name (read-only)
The master.cf service name of a Postfix daemon process.

Available in Postfix 3.5 and later:

info_log_address_format (external)
The email address form that will be used in non-debug logging (info, warning, etc.).

SEE ALSO
qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
postlogd(8), Postfix logging
syslogd(8), system logging

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

Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA

PIPE(8postfix)