setting up groups in sendmail
 

I'm trying to find a simple way to setup mail groups in sendmail. I need to set up a total of about 40 groups, each group will contain anywhere from 5 to 60 users so using the aliases file would be very time consuming, and I'd like to avoid it if possible. If I could I'd like to be able to use the user groups so I can have a primary and secondary group for each user, so the primary group can be all the users in a building and the secondary group can be a certain department in the building.

Can someone tell me the simplest way to do this? I've seen a lot of people suggest using postfix instead of sendmail. If postfix will do this how hard is it to switch from sendmail to postfix?

Why not use a mailing list server like mailman:
http://www.list.org

I'm having some problems getting mailman to work, but if that's the best suggestion, I'll keep at it. The easiest way would be for my users to create the groups themselves, but my boss wants it set up so they don't have to.