Well, I hardly call it a "problem" just simply a feature that hasn't been added yet since there is so much to it...
If a solution where thought up, ideally it'd have to support POP3, IMAP, and EMail Piping (as lots of users don't host email on the same server or just don't have access to the nitty gritty to be able to support email piping)...
so it's all in all a LOT of work to be done... Especially for free