For retrieving mail from relatively locked-down Exchange servers, that only permit OWA access, it very easily allows me to 'break out' of the box the IT guys want to put me in, and use rational tools and protocols like IMAP, POP, SMTP and Thunderbird to send/retrieve mail from the Exchange server.
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.
