I've attached a utility to interface the Courier MTA with mailman for possible
inclusion in the contrib section of the Mailman distribution. This is rather
similar to qmail-to-mailman.py with a few changes to the code to accommodate
differences between the the two MTAs and a number of changes to the
instructions in the comments. This script has worked flawlessly for me for
over 5 years, so it's been well tested.

Note, of course, that a line will need to be added to configure.in (and
configure, implicitly, via autoconf) to copy the file and replace tokens used
in the attached script with actual paths.

Courier is actively supported and development on it is ongoing, whereas qmail
is unsupported and largely deprecated for use in new mail server
installations.