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 ex-
panded 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 re-
quest. Examples are pagers or fax machines. In addition, multi-recipi-
ent delivery is undesirable when prepending a Delivered-to: or X-Origi-
nal-To: message header.
To prevent Postfix from sending multiple recipients per delivery re-
quest, 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 trans-
port.
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 op-
tional 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 com-
mand. The directory must be accessible for the user specified
with the user attribute (see below). The default working direc-
tory 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 recog-
nized: \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 deliv-
ery. 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 com-
mand-line $sender, $original_recipient and $recipient ad-
dress 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 com-
mand-line recipients by the Postfix sendmail(1) mail sub-
mission 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 deliv-
ery via UUCP.
. Prepend "." to lines starting with ".". This is needed by,
for example, BSMTP software.
> Prepend ">" to lines starting with "From ". This is ex-
pected by, for example, UUCP software.
null_sender=replacement (default: MAILER-DAEMON)
Replace the null sender address (typically used for delivery sta-
tus notifications) with the specified text when expanding the
$sender command-line macro, and when generating a From_ or Re-
turn-Path: message header.
If the null sender replacement text is a non-empty string then it
is affected by the q flag for address quoting in command-line ar-
guments.
The null sender replacement text may be empty; this form is rec-
ommended for content filters that feed mail back into Postfix.
The empty sender address is not affected by the q flag for ad-
dress quoting in command-line arguments.
Caution: a null sender address is easily mis-parsed by naive
software. For example, when the pipe(8) daemon executes a command
such as:
Wrong: command -f$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 $recipi-
ent.
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. with-
out interpretation of shell meta characters by a shell command
interpreter.
Specify "{" and "}" around command arguments that contain white-
space, arguments that begin with "{", or arguments that must be
an empty string (Postfix 3.0 and later). The outer "{" and "}"
will be removed, together with any leading or trailing whitespace
in the remaining text.
In the command argument vector, the following macros are recog-
nized and replaced with corresponding information from the Post-
fix queue manager delivery request.
In addition to the form ${name}, the forms $name and the depre-
cated form $(name) are also recognized. Specify $$ where a sin-
gle $ 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 para-
meter.
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 fold-
ing.
This feature is available as of Postfix 2.5.
${envid}
This macro expands to the RFC 3461 envelope ID if avail-
able, otherwise the empty string.
This feature is available as of Postfix 3.9.
${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 recipi-
ents.
This information is modified by the u flag for case fold-
ing.
${mailbox}
This macro expands to the complete local part of a recipi-
ent 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 fold-
ing.
${nexthop}
This macro expands to the next-hop hostname.
This information is modified by the h flag for case fold-
ing.
${original_recipient}
This macro expands to the complete recipient address be-
fore any address rewriting or aliasing.
A command-line argument that contains ${original_recipi-
ent} 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 orig-
inal 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 com-
mand 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 de-
fault, the null sender address expands to MAILER-DAEMON;
this can be changed with the null_sender attribute, as de-
scribed 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 ad-
dress. For example, with an address user+foo@domain the
username part is user.
A command-line argument that contains ${user} expands into
as many command-line arguments as there are recipients.
This information is modified by the u flag for case fold-
ing.
STANDARDS
RFC 3463 (Enhanced status codes)
DIAGNOSTICS
Command exit status codes are expected to follow the conventions defined
in <sysexits.h>. Exit status 0 means normal successful completion.
In the case of a non-zero exit status, a limited amount of command out-
put is logged, and reported in a delivery status notification. When the
output begins with a 4.X.X or 5.X.X enhanced status code, the status
code takes precedence over the non-zero exit status (Postfix version 2.3
and later).
After successful delivery (zero exit status) a limited amount of command
output is logged, and reported in "success" delivery status notifica-
tions (Postfix 3.0 and later). This command output is not examined for
the presence of an enhanced status code.
Problems and transactions are logged to syslogd(8) or postlogd(8). Cor-
rupted message files are marked so that the queue manager can move them
to the corrupt queue for further inspection.
SECURITY
This program needs a dual personality 1) to access the private Postfix
queue and IPC mechanisms, and 2) to execute external commands as the
specified user. It is therefore security sensitive.
CONFIGURATION PARAMETERS
Changes to main.cf are picked up automatically as pipe(8) processes run
for only a limited amount of time. Use the command "postfix reload" to
speed up a change.
The text below provides only a parameter summary. See postconf(5) for
more details including examples.
RESOURCE AND RATE CONTROLS
In the text below, transport is the first field in a master.cf entry.
transport_time_limit ($command_time_limit)
A transport-specific override for the command_time_limit parame-
ter value, where transport is the master.cf name of the message
delivery transport.
Implemented in the qmgr(8) daemon:
transport_destination_concurrency_limit ($default_destination_concur-
rency_limit)
A transport-specific override for the default_destination_concur-
rency_limit parameter value, where transport is the master.cf
name of the message delivery transport.
transport_destination_recipient_limit ($default_destination_recipi-
ent_limit)
A transport-specific override for the default_destination_recipi-
ent_limit parameter value, where transport is the master.cf name
of the message delivery transport.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf config-
uration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a re-
quest 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
delay values.
export_environment (see 'postconf -d' output)
The list of environment variables that a Postfix process will ex-
port to non-Postfix processes.
ipc_timeout (3600s)
The time limit for sending or receiving information over an in-
ternal 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 local-
part, 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 de-
livery status code or explanatory text of successful or unsuc-
cessful deliveries.
Available in Postfix version 3.3 and later:
enable_original_recipient (yes)
Enable support for the original recipient address after an ad-
dress 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)
Generated by dwww version 1.16 on Tue Dec 16 04:31:27 CET 2025.