If I might add something here....
I was one of the beta sites in GList's development. I paid Gossamer Threads
(GT) write a plugin (I think Stone actually wrote it) that would allow a certain amount of this kind of function. My goal was to use GList as a re-mailer or mail forwarding mechanism. Our groups maintains several different mailing lists and he wrote it such that you could mail to an account (POP3) and GList would sweep that account and forward to the mailing list assigned to that POP3 account. Kinda like Mailarc in GForum, but instead posting an email to a forum, this MailArc sends the message out to a GList mail group.
I can see how this could work as a discussion list (like MajorDomo, etc.). But that's not what I wanted. Maybe this could be modified (by you or possibly GT for a fee
) to provide the functionality you desire.