The part that would be easy-peasy on Linux (or other unixen) is emailing out the turns. You just write a shell script that calls elm, or mail, or pine (is that the usenet one?) to send the right turn to the right player every time.
As far as the rest goes, I used to use procmail for spam filtering about 5 years ago, but haven't a brain cell remaining that would rememember how to do such things. Especially since all _I_ was using procmail for was to throw away email, not extract attachments.
