Updated: 2022/Sep/29
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PIPE(8) System Manager's Manual PIPE(8)
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 definition. 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 before 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 failure.
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 insensitive.
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_recipient_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 entire 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 recommended 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
$sender command-line macro, and when generating a From_ or
Return-Path: message header.
If the null sender replacement text is a non-empty string then
it is affected by the q flag for address quoting in command-line
arguments.
The null sender replacement text may be empty; this form is
recommended for content filters that feed mail back into
Postfix. The empty sender address is not affected by the q flag
for address quoting in command-line arguments.
Caution: a null sender address is easily mis-parsed by naive
software. For example, when the pipe(8) daemon executes a
command such as:
Wrong: command -f$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
NOTE: DO NOT put quotes around the command, $sender, or
$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 example, 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 command-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 example, with an address
user+foo@domain the mailbox is user+foo.
A command-line argument that contains ${mailbox} expands
to as many command-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 rewriting 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 command-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
attribute, 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 approximation 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 ${user} expands
into as many command-line arguments as there are
recipients.
This information is modified by the u flag for case
folding.
STANDARDS
RFC 3463 (Enhanced status codes)
DIAGNOSTICS
Command exit status codes are expected to follow the conventions
defined in <sysexits.h>. Exit status 0 means normal successful
completion.
In the case of a non-zero exit status, a limited amount of command
output is logged, and reported in a delivery status notification. When
the output begins with a 4.X.X or 5.X.X enhanced status code, the
status code takes precedence over the non-zero exit status (Postfix
version 2.3 and later).
After successful delivery (zero exit status) a limited amount of
command output is logged, and reported in "success" delivery status
notifications (Postfix 3.0 and later). This command output is not
examined for the presence of an enhanced status code.
Problems and transactions are logged to syslogd(8) or postlogd(8).
Corrupted message files are marked so that the queue manager can move
them to the corrupt queue for further inspection.
SECURITY
This program needs a dual personality 1) to access the private Postfix
queue and IPC mechanisms, and 2) to execute external commands as the
specified user. It is therefore security sensitive.
CONFIGURATION PARAMETERS
Changes to main.cf are picked up automatically as pipe(8) processes run
for only a limited amount of time. Use the command "postfix reload" to
speed up a change.
The text below provides only a parameter summary. See postconf(5) for
more details including examples.
RESOURCE AND RATE CONTROLS
In the text below, transport is the first field in a master.cf entry.
transport_time_limit ($command_time_limit)
A transport-specific override for the command_time_limit
parameter value, where transport 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 terminated 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 an email address
localpart, user name, or a .forward file name from its
extension.
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 example, "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(8)