SENDMAIL(1)

📦
version 3.10.14 · 3 versions
, in fedora 43, fedora 44

💌 SENDMAIL(1) 💌

okay bestie, gather round, because this is sendmail from the General Commands Manual and it is lowkey iconic — it's the Postfix to Sendmail compatibility interface. yes, that means it speaks fluent Old Sendmail so your ancient scripts don't have a meltdown 🫶

📛 NAME

sendmail — Postfix to Sendmail compatibility interface

📜 SYNOPSIS

sendmail [option ...] [recipient ...]

mailq
sendmail -bp

newaliases
sendmail -I

🦋 DESCRIPTION

The Postfix sendmail(1) command implements the Postfix to Sendmail compatibility interface. And because existing applications are out here living their lives, some Sendmail command-line options are recognized but silently ignored. they just get a lil nod and then we move on 💅

By default, Postfix sendmail(1) reads a message from standard input until EOF, or until it reads a line with only a . character, and then arranges for delivery. It leans on the postdrop(1) command to create a queue file in the maildrop directory. teamwork makes the dream work ✨

Specific command aliases are provided for other common modes of operation:

  • mailq — List the mail queue. Each entry shows the queue file ID, message size, arrival time, sender, and the recipients that still need to be delivered. If mail could not be delivered upon the last attempt, the reason for failure is shown. The queue ID string is followed by an optional status character:
    • * — The message is in the active queue, i.e. the message is selected for delivery.
    • ! — The message is in the hold queue, i.e. no further delivery attempt will be made until the mail is taken off hold.
    • # — The message is forced to expire. See the postsuper(1) options -e or -f.

This mode of operation is implemented by executing the postqueue(1) command.

  • newaliases — Initialize the alias database. If no input file is specified (with the -oA option, see below), the program processes the file(s) specified with the alias_database configuration parameter. If no alias database type is specified, the program uses the type specified with the default_database_type configuration parameter. This mode of operation is implemented by running the postalias(1) command.
Note: it may take a minute or so before an alias database update becomes visible. Use the "postfix reload" command to eliminate this delay. (the way that one command just fixes your whole patience problem 😭)

These and other features can be selected by specifying the appropriate combination of command-line options. Some features are controlled by parameters in the main.cf configuration file.

The following options are recognized:

✨ OPTIONS ✨

  • -Am — (ignored) 🙈
  • -Ac — (ignored). Postfix sendmail uses the same configuration file regardless of whether or not a message is an initial submission.
  • -B body_type — The message body MIME type: 7BIT or 8BITMIME.
  • -bd — Go into daemon mode. This mode of operation is implemented by executing the "postfix start" command.
  • -bh — (ignored) 🙈
  • -bH — (ignored). Postfix has no persistent host status database. (no memory, no drama, we simply forget 🧚)
  • -bi — Initialize alias database. See the newaliases command above.
  • -bl — Go into daemon mode. To accept only local connections as with Sendmail's -bl option, specify "inet_interfaces = loopback" in the Postfix main.cf configuration file.
  • -bm — Read mail from standard input and arrange for delivery. This is the default mode of operation. 👑
  • -bp — List the mail queue. See the mailq command above.
  • -bs — Stand-alone SMTP server mode. Read SMTP commands from standard input, and write responses to standard output. In stand-alone SMTP server mode, mail relaying and other access controls are disabled by default. To enable them, run the process as the mail_owner user.

This mode of operation is implemented by running the smtpd(8) daemon.

  • -bv — Do not collect or deliver a message. Instead, send an email report after verifying each recipient address. This is useful for testing address rewriting and routing configurations.

This feature is available in Postfix version 2.1 and later.

  • -C config_file
  • -C config_dir — The path name of the Postfix main.cf file, or of its parent directory. This information is ignored with Postfix versions before 2.3.

With Postfix version 3.2 and later, a non-default directory must be authorized in the default main.cf file, through the alternate_config_directories or multi_instance_directories parameters.

With all Postfix versions, you can specify a directory pathname with the MAIL_CONFIG environment variable to override the location of configuration files.

  • -F full_name — Set the sender full name. This overrides the NAME environment variable, and is used only with messages that have no From: message header.
  • -f sender — Set the envelope sender address. This is the address where delivery problems are sent to. With Postfix versions before 2.1, the Errors-To: message header overrides the error return address.
  • -G — Gateway (relay) submission, as opposed to initial user submission. Either do not rewrite addresses at all, or update incomplete addresses with the domain information specified with remote_header_rewrite_domain.

This option is ignored before Postfix version 2.3.

  • -h hop_count — (ignored). Hop count limit. Use the hopcount_limit configuration parameter instead.
  • -I — Initialize alias database. See the newaliases command above.
  • -i — When reading a message from standard input, don't treat a line with only a . character as the end of input.
  • -L label — (ignored). The logging label. Use the syslog_name configuration parameter instead.
  • -m — (ignored). Backwards compatibility.
  • -N dsn — (default: 'delay, failure') Delivery status notification control. Specify either a comma-separated list with one or more of failure (send notification when delivery fails), delay (send notification when delivery is delayed), or success (send notification when the message is delivered); or specify never (don't send any notifications at all).

This feature is available in Postfix 2.3 and later.

  • -n — (ignored). Backwards compatibility.
  • -oAalias_database — Non-default alias database. Specify pathname or type:pathname. See postalias(1) for details.
  • -O option=value — (ignored). Set the named option to value. Use the equivalent configuration parameter in main.cf instead.
  • -o7 — (ignored) 🙈
  • -o8 — (ignored). To send 8-bit or binary content, use an appropriate MIME encapsulation and specify the appropriate -B command-line option.
  • -oi — When reading a message from standard input, don't treat a line with only a . character as the end of input.
  • -om — (ignored). The sender is never eliminated from alias etc. expansions.
  • -o x value — (ignored). Set option x to value. Use the equivalent configuration parameter in main.cf instead.
  • -r sender — Set the envelope sender address. This is the address where delivery problems are sent to. With Postfix versions before 2.1, the Errors-To: message header overrides the error return address.
  • -R return — Delivery status notification control. Specify "hdrs" to return only the header when a message bounces, "full" to return a full copy (the default behavior).

The -R option specifies an upper bound; Postfix will return only the header, when a full copy would exceed the bounce_size_limit setting.

This option is ignored before Postfix version 2.10.

  • -q — Attempt to deliver all queued mail. This is implemented by executing the postqueue(1) command.
Warning: flushing undeliverable mail frequently will result in poor delivery performance of all other mail. (fr fr, don't spam the flush button bestie 💀)
  • -qinterval — (ignored). The interval between queue runs. Use the queue_run_delay configuration parameter instead.
  • -qIqueueid — Schedule immediate delivery of mail with the specified queue ID. This option is implemented by executing the postqueue(1) command, and is available with Postfix version 2.4 and later.
  • -qRsite — Schedule immediate delivery of all mail that is queued for the named site. This option accepts only site names that are eligible for the "fast flush" service, and is implemented by executing the postqueue(1) command. See flush(8) for more information about the "fast flush" service.
  • -qSsite — This command is not implemented. Use the slower "sendmail -q" command instead. (we love an honest icon 🫶)
  • -t — Extract recipients from message headers. These are added to any recipients specified on the command line.

With Postfix versions prior to 2.1, this option requires that no recipient addresses are specified on the command line.

  • -U — (ignored). Initial user submission.
  • -V envid — Specify the envelope ID for notification by servers that support DSN.

This feature is available in Postfix 2.3 and later.

  • -XV — (Postfix 2.2 and earlier: -V) Variable Envelope Return Path. Given an envelope sender address of the form owner-listname@origin, each recipient user@domain receives mail with a personalized envelope sender address.

By default, the personalized envelope sender address is owner-listname+user=domain@origin. The default + and = characters are configurable with the default_verp_delimiters configuration parameter.

  • -XVxy — (Postfix 2.2 and earlier: -Vxy) As -XV, but uses x and y as the VERP delimiter characters, instead of the characters specified with the default_verp_delimiters configuration parameter.
  • -v — Send an email report of the first delivery attempt (Postfix versions 2.1 and later). Mail delivery always happens in the background. When multiple -v options are given, enable verbose logging for debugging purposes.
  • -X log_file — (ignored). Log mailer traffic. Use the debug_peer_list and debug_peer_level configuration parameters instead.

and that's only part one, bestie — there is SO much more coming, don't you dare close the tab 💜

🔒 SECURITY 🔒

okay bestie, this is the part where we get serious for a sec, because it's giving "safety briefing" energy and you need to actually read it 💅

By design, this program is not set-user (or group) id. She's built different — she's prepared to handle message content from untrusted, possibly remote, users. 😌

However. And this is a big however, like, main-character-plot-twist however: like most Postfix programs, this one does not enforce a security policy on its command-line arguments. Nope. Instead, she relies on the UNIX system to enforce access policies based on the effective user and group IDs of the process. Concretely, this means that running Postfix commands as root (from sudo or equivalent) on behalf of a non-root user is likely to create privilege escalation opportunities. 🚨

fr fr, that's the dangerous bit. not exaggerating, not being dramatic. that's a real "privilege escalation" situation and privilege escalation is never a vibe.

If an application runs any Postfix programs on behalf of users that do not have normal shell access to Postfix commands, then that application MUST restrict user-specified command-line arguments to avoid privilege escalation. No cap, this is a MUST.

  • Filter all command-line arguments, for example arguments that contain a pathname or that specify a database access method. These pathname checks must reject user-controlled symlinks or hardlinks to sensitive files, and must not be vulnerable to TOCTOU race attacks. 🕵️♀️
  • Disable command options processing for all command arguments that contain user-specified data. For example, the Postfix sendmail(1) command line MUST be structured as follows:
/path/to/sendmail system-arguments -- user-arguments

Here, the -- disables command option processing for all user-arguments that follow. 🛑

Without the --, a malicious user could enable Postfix sendmail(1) command options, by specifying an email address that starts with -. And like, an email address starting with a dash should just be a weird email address, not a secret cheat code for your flags. 🙈

🩺 DIAGNOSTICS 🩺

Problems are logged to syslogd(8) or postlogd(8), and to the standard error stream. So when something's wrong, she's not ghosting you — she's logging it in three different places, lowkey thorough of her. ✨

🌱 ENVIRONMENT 🌱

  • MAIL_CONFIG — Directory with Postfix configuration files. 📁
  • MAIL_VERBOSE (value does not matter) — Enable verbose logging for debugging purposes. She's gonna talk. A lot. 🗣️
  • MAIL_DEBUG (value does not matter) — Enable debugging with an external command, as specified with the debugger_command configuration parameter. 🔍
  • NAME — The sender full name. This is used only with messages that have no From: message header. See also the -F option above. 💌

⚙️ CONFIGURATION PARAMETERS ⚙️

The following main.cf parameters are especially relevant to this program. The text below provides only a parameter summary — like, the lil sparknotes version. See postconf(5) for more details including examples, because she wrote a whole essay over there. 📚

🧩 COMPATIBILITY CONTROLS

Available with Postfix 2.9 and later:

  • sendmail_fix_line_endings (always) — Controls how the Postfix sendmail command converts email message line endings from <CR><LF> into UNIX format (<LF>). cute little glow-up for your line endings. ✨

🛠️ TROUBLE SHOOTING CONTROLS

The DEBUG_README file gives examples of how to troubleshoot a Postfix system. (We'll get to README_FILES later, keep scrolling bestie 💜)

  • debugger_command (empty) — The external command to execute when a Postfix daemon program is invoked with the -D option.
  • debug_peer_level (2) — The increment in verbose logging level when a nexthop destination, remote client or server name or network address matches a pattern given with the debug_peer_list parameter.
  • debug_peer_list (empty) — Optional list of nexthop destination, remote client or server name or network address patterns that, if matched, cause the verbose logging level to increase by the amount specified in $debug_peer_level.

🔐 ACCESS CONTROLS

Available in Postfix version 2.2 and later:

  • authorized_flush_users (static:anyone) — List of users who are authorized to flush the queue.
  • authorized_mailq_users (static:anyone) — List of users who are authorized to view the queue. 👀
  • authorized_submit_users (static:anyone) — List of users who are authorized to submit mail with the sendmail(1) command (and with the privileged postdrop(1) helper command).

⚖️ RESOURCE AND RATE CONTROLS

  • bounce_size_limit (50000) — The maximal amount of original message text that is sent in a non-delivery notification.
  • fork_attempts (5) — The maximal number of attempts to fork() a child process.
  • fork_delay (1s) — The delay between attempts to fork() a child process.
  • hopcount_limit (50) — The maximal number of Received: message headers that is allowed in the primary message headers. 🛣️
  • queue_run_delay (300s) — The time between deferred queue scans by the queue manager; prior to Postfix 2.4 the default value was 1000s. (yes, she changed her mind in 2.4, growth era 💅)

🏃♀️ FAST FLUSH CONTROLS

The ETRN_README file describes configuration and operation details for the Postfix "fast flush" service. ⚡

  • fast_flush_domains ($relay_domains) — Optional list of destinations that are eligible for per-destination logfiles with mail that is queued to those destinations.

🦋 VERP CONTROLS

The VERP_README file describes configuration and operation details of Postfix support for variable envelope return path addresses.

  • default_verp_delimiters (+=) — The two default VERP delimiter characters.
  • verp_delimiter_filter (-=+) — The characters Postfix accepts as VERP delimiter characters on the Postfix sendmail(1) command line and in SMTP commands.

🎀 MISCELLANEOUS CONTROLS

  • alias_database (see postconf -d output) — The alias databases for local(8) delivery that are updated with "newaliases" or with "sendmail -bi".
  • command_directory (see postconf -d output) — The location of all postfix administrative commands.
  • config_directory (see postconf -d output) — The default location of the Postfix main.cf and master.cf configuration files.
  • daemon_directory (see postconf -d output) — The directory with Postfix support programs and daemon programs.
  • default_database_type (see postconf -d output) — The default database type for use in newaliases(1), postalias(1) and postmap(1) commands.
  • delay_warning_time (0h) — The time after which the sender receives a copy of the message headers of mail that is still queued.
  • import_environment (see postconf -d output) — The list of environment variables that a privileged Postfix process will import from a non-Postfix parent process, or name=value environment overrides.
  • mail_owner (postfix) — The UNIX system account that owns the Postfix queue and most Postfix daemon processes. 👑
  • queue_directory (see postconf -d output) — The location of the Postfix top-level queue directory.
  • remote_header_rewrite_domain (empty) — Rewrite or add message headers in mail from remote clients if the remote_header_rewrite_domain parameter value is non-empty, updating incomplete addresses with the domain specified in the remote_header_rewrite_domain parameter, and adding missing headers.
  • 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".

Postfix 3.2 and later:

  • alternate_config_directories (empty) — A list of non-default Postfix configuration directories that may be specified with "-c config_directory" on the command line (in the case of sendmail(1), with the "-C" option), or via the MAIL_CONFIG environment parameter.
  • multi_instance_directories (empty) — An optional list of non-default Postfix configuration directories; these directories belong to additional Postfix instances that share the Postfix executable files and documentation with the default Postfix instance, and that are started, stopped, etc., together with the default Postfix instance.

📂 FILES 📂

  • /var/spool/postfix, mail queue 📬
  • /etc/postfix, configuration files 🗂️

👀 SEE ALSO 👀

📖 README_FILES 📖

Use "postconf readme_directory" or "postconf html_directory" to locate this information. ✨

  • DEBUG_README, Postfix debugging howto
  • ETRN_README, Postfix ETRN howto
  • VERP_README, Postfix VERP howto

📜 LICENSE 📜

The Secure Mailer license must be distributed with this software. periodt. 💅

💖 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

and that's a wrap on the SENDMAIL(1) page bestie!! 🎀 this was the Postfix sendmail(1) manual page, and yes, the same legend Wietse Venema wrote both of those addresses, king behavior honestly 👑 go forth and send your mail responsibly, always use that --, and stay hydrated 🦋💜

📦 where this page comes from