I have no idea. I haven't worked with Python in several years. But, I know that both Mailman and Trac are written in Python and they both do stuff with incoming mail...so, there's certainly some python code out their for dealing with incoming mail. That's where I'd start my search if I were in your shoes.

one way to do it is to use procmail to filter incoming mail and piping the ones you are interested into your python program which will take the rfc822 message on stdin. the email module (http://docs.python.org/lib/module-email.html) will let you parse these messages.

this is provided that your MX dns entry points to your machine and that you have the appropriate ports unlocked, of course.