extsmail

Overview

extsmail masquerades as the standard UNIX sendmail program, reading messages, and piping them to user-defined commands until sending succeeds. It is particularly useful if you want to send email via commands that assume a fault-free network, for example via msmtp (to an external SMTP server) or ssh (to a server running a full sendmail-compatible MTA). extsmail is not a full SMTP server. It doesn't need root privileges. It can run as a daemon, or as a batch job (e.g. via cron). It is designed to have sensible defaults, and configuring it is a quick, one-off job.

Download and docs

• Latest release: extsmail-2.7 (2022-10-19)
  • Size: 70722 bytes (69KiB)
  • SHA256: +ZKf/Xx0v653kwZo843dxcMsfO/9ELKEP/3wjWfIH3k=
  • Release notes:
    
    • Introduce a test suite for (unusual) child process failure modes.
    • Ensure that all of a child processes's stderr output is read, even if another failure (e.g. the child prematurely closing stdin) occurs beforehand. This makes debugging failing child processes easier.
    • Treat child processes killed by a signal as unsuccessful.
    • Introduce a timeout for child processes that, after seemingly processing a file correctly (e.g. consuming all input, closing the relevant file descriptors), then stall before exiting.
• All releases
• Repository (issues, PRs, etc.)
• Documentation:
  • Manual
  • FAQ
  • Configuring other apps to use extsmail
  • Exotic scenarios using extsmail
• Man pages:
  • extsmail(1)
  • extsmail.conf(5)
  • extsmail.externals(5)
  • extsmaild(1)
• Related programs

60 second install instructions

If you don't like reading manuals, most per-user configurations of extsmail can be accommodated with the following commands:

$ ./configure
$ make
$ make install
$ mkdir -m 700 -p ~/.extsmail/spool_dir
$ echo spool_dir = \"~/.extsmail/spool_dir\" > ~/.extsmail/conf

If you want to send e-mail to another machine via ssh, you then need to create the file ~/.extsmail/externals and put in the following configuration:

group {
    external mymachine {
        sendmail = "/usr/bin/ssh -q -C -l user mymachine.net /usr/sbin/sendmail -t"
    }
}

where mymachine is a human-friendly name given to an external (it does not effect processing), and user is your username on the remote machine mymachine.net.

If instead you want to use msmtp, your ~/.extsmail/externals file will look as follows:

group {
    external mymachine {
        sendmail = "/usr/local/bin/msmtp -a myaccount"
    }
}

where mymachine is a human-friendly name given to an external (it does not effect processing), and myaccount is the msmtp account you want to send mail as.

You can then run extsmaild either as a batch mode process (e.g. from cron) or, generally better, as a daemon, started from a start-up script (e.g. ~/.xsession):

extsmaild -m daemon

You then need to configure whatever programs you're using to send mail to use extsmail instead of your normal sendmail binary. extsmaild will use syslog for logging (typically logging into /var/log/maillog).

And with that you're done. If you want to do something more complex you'll need to read the detailed instructions (extsmail comes with complete man page documentation), but the above works perfectly well for the majority of cases.

Install

extsmail is a C application. It should be trivially portable to any POSIX compliant operating system. It can be installed as follows:

$ ./configure
$ make
$ make install

Please note that if, and only if, you are building from the git repository you will first need to execute make -f Makefile.bootstrap to build the configure script.

Credits

extsmail was originally created by Laurence Tratt. Olivier Girondel has been a major contributor since v1.8.