I suggest you look at the Mail::Box module anyway. It is written in a way that is generic - it asbtracts the Mailbox - and is independent of the transport (which is POP3 in my case).

You may be able to use the Message and Messager-header objects, or subclass them. Or at least get some ideas on how to structure mail - like I said - this is a very-well designed module, worth a peek.