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pipe - Unix, Linux Command


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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 external commands cannot handle more than one recipient per delivery request. Examples of such transports are pagers or fax machines.

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

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.

This feature is available as of Postfix 2.0.

R Prepend a Return-Path: message header with the envelope sender address.
h Fold the command-line $recipient domain name and $nexthop host name to lower case. This is recommended for delivery via UUCP.
q Quote white space and other special characters in the command-line $sender 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 $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, which is 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:

   command -f$sender -- $recipient (bad)

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:

   command -f $sender -- $recipient (good)

This feature is available with Postfix 2.3 and later.

size=size_limit (optional) Messages greater in size than this limit (in bytes) will be returned to the sender as undeliverable.
user=username (required)
user=username:groupname Execute the external command with the rights 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.

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 $(name) are also recognized. Specify $$ where a single $ is wanted.

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

This is available in Postfix 2.2 and later.

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

This is available in Postfix 2.2 and later.

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

This is available in Postfix 2.2 and later.

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

This is available in Postfix 2.2 and later.

${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.

${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 SASL authentication mechanism used during the reception of the message. An empty string is passed if the message has been received without SASL authentication.

This is available in Postfix 2.2 and later.

${sasl_sender} This macro expands to the SASL sender name (i.e. the original submitter as per RFC 2554) used during the reception of the message.

This is available in Postfix 2.2 and later.

${sasl_username} This macro expands to the SASL user name used during the reception of the message. An empty string is passed if the message has been received without SASL authentication.

This is available in Postfix 2.2 and later.

${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.

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.

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 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.
TagDescription
transport_destination_concurrency_limit ($default_destination_concurrency_limit) Limit the number of parallel deliveries to the same destination, for delivery via the named transport. The limit is enforced by the Postfix queue manager.
transport_destination_recipient_limit ($default_destination_recipient_limit) Limit the number of recipients per message delivery, for delivery via the named transport. The limit is enforced by the Postfix queue manager.
transport_time_limit ($command_time_limit) Limit the time for delivery to external command, for delivery via the named transport. The limit is enforced by the pipe delivery agent.

MISCELLANEOUS CONTROLS


TagDescription
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 the next service request before exiting.
max_use (100) The maximal number of connection requests before a Postfix daemon process terminates.
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 separator between user names and address extensions (user+foo).
syslog_facility (mail) The syslog facility of Postfix logging.
syslog_name (postfix) The mail system name that is prepended to the process name in syslog records, so that "smtpd" becomes, for example, "postfix/smtpd".

SEE ALSO

qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
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


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