femtomail is a minimal Mail Delivery Agent (MDA) for local mail. Mail is accepted from standard input and placed in a Maildir box of a user. This software is intended for use on a single-user machine.

Remote delivery, daemonizing, sender verification, etc. is not implemented and won't be implemented due to its complexity. femtomail is not written because mail software did not exist, but because existing software were too large for the simple task of delivering cron mail to the local user.

The workflow of femtomail:

1. Change the process user and group.
2. Create a new file with a unique filename in the mail directory.
3. Write a Received header to the file. If From and Date headers are missing, then they will also be appended to the headers.
4. Pass data from standard input to the file.
5. Exit.

femtomail can replace the sendmail binary, but note that delivery is only possible for a single user. When invoked as newaliases or mailq, the program exits with a zero status code. Most options of sendmail are ignored except for the -fname and address arguments. Only the -bm mode (read from stdin and deliver the usual way) is supported, femtomail will exit in other modes.

The user to deliver mail to has to be specified at compile time:

make USERNAME=peter

By default, the Maildir directory is ~/.local/share/local-mail/inbox. It can be changed to ~/.Maildir/inbox as follows:

make USERNAME=peter MAILBOX_PATH=.Maildir/inbox

Absolute paths are also supported. The following configuration will put mail in /var/mail/new/(filename):

make USERNAME=nobody MAILBOX_PATH=/var/mail

To install femtomail on your system with the appropriate capabilities:

make install install-link-sendmail setcap
# You must manually create the mailbox if it does not exist yet
mkdir -p ~/.local/share/local-mail/inbox

Note: the femtomail binary must be installed with file capabilities set (recommended). Alternatively, the program can run with setuid-root. Either way, the user and groups are changed before the mail is read and written.

If you do not have appropriate privileges to install femtomail (you are not root) or if you want to try it out before installing, then you can specify the program as sendmail program for the mail program (from heirloom-mailx).

Example (assuming that femtomail is built and available in the current working directory):

echo Testing... | mail -S sendmail=femtomail -s Subject peter

Not much validation is done for the address specified with the -f option or the recipient address. The mail body is passed unprocessed. If femtomail is invoked without specifying mail contents, an empty message will be created. If the mail does not contain headers, Date and From headers will be appended anyway.

Other bugs can be reported at <[email protected]>.

Copyright (c) 2013-2015 Peter Wu <[email protected]>

License: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.