I have a client that is using a listserver account to facilitate communication between members. They want to add archiving of messages functionality, so I tried to get them using a Google Group. Overall the Google Group worked well, but there are a few things that didn't quite mesh with what they wanted. Does anybody know any alternatives to Google Groups?

High level requirements:
1) Most communication is done through email, so that "listserver" functionality needs to remain.
2) All posts must be moderated before being public.
3) Messages and subject lines must be able be edited by admins.

That's really about it... Thanks for any help!