I've posted my courier-to-mailman.py file for public download at <http://www.fmp.com/downloads/courier-to-mailman.py>. It's mostly the same as Bruce Perens' qmail-to-mailman.py with a few bug fixes and changes to accomodate courier's slightly different set of exit codes. There are 3 system-specific variables that need to be set near the start of the file, and the file comments contain complete usage instructions. This program is in use on a daily basis for a bunch of production mailing lists, so I know it's good code.