I think it would be a great feature to add to the Forum module, to be able to to configure a POP3 mailbox to poll, periodically, for new messages that would then be posted to a forum. Used in conjunction with a "fake" user that subscribes to notification emails for the forum, this would make it much easier to convince communities that are currently using something like Yahoo! Groups to switch over to DNN. The members of the group could gradually migrate over, rather than requiring a major exodus all at once.

I took a quick peek at the database schema, and decided it was too complicated to whip up a quick solution, on my own. "Maybe someday," when I get some spare time I'll dig into it... eventually, though, I think this would be a valuable feature to include in the core module.