Update 2013: I've been using this DavMail OSS software for a few years now and it's really great. If it works as claimed, I can point any mail client to it and it will sync my mail in two directions so I can send messages that will pass through the system and see all the messages that come in. This appears to be a POP3/IMAP and SMTP bridge to activesync which is exactly what I want. Probably where I should have posted to begin with (I swear I googled before posting but apparently not enough). Ok - of course 20 seconds after posting this, I find an answer on superuser.
