I have a dirty secret.
I have an Exchange server and I like it. A lot.
I started down the road to an Exchange server with the introduction of DirectPush on Windows Mobile (I've talked before about how well DirectPush works, so I won't go into that here). DirectPush required me to have an Exchange account, which I got through 4SmartPhone.net. This all worked well, except that I have several email accounts, and 4SmartPhone.net will only retrieve and forward mail from one. Further, with the outrageous GPRS pricing, I'm completely unwilling to pay to ship spam over-the-air, and their anti-spam protection was letting too many slip through.
Coincidentally, I realized that I had a perfectly good (if slightly underpowered) test server running Windows Server 2003 and Exchange 2003.
First off was to find a way to grab the email out of my various POP accounts and forward it to my Exchange account. I ended up using GetMail 4 Hotmail running as a service (to start out with, at least). This utility periodically grabs email out of POP accounts and forwards them to the appropriate email address via SMTP (i.e. the local Exchange server). The only complaint I have about this methodology is that I have to regularly remove the messages from the POP servers myself. I'm looking at using Fetchmail instead. For the time being though, it's working well.
I set up Spam Assassin to perform spam filtering; using the excellent SpamAssassin Sink to integrate it with Exchange. It was reasonably easy to set up, although I have to find a better way of updating the Bayesian tokens than running batch scripts manually.
Finally, I turned on DirectPush. I've set up Blackberry BES servers before, and the difference in configuration is night and day. Basically you check a checkbox and you're good to go.
I've been running this configuration for a few weeks now in parallel with my "normal" mail configuration (i.e. a mail client contacting various POP servers). I've had nothing but success so far (I received all of my email while at the WWDC on my JasJar via Cingular wireless) and I have vastly less spam delivered than I would normally get through Apple Mail.
Once I get the Pop->Exchange procedure running to my satisfaction, I expect to switch over completely.
Suggested reading:
Configure Exchange 2003 Server
Hotmail Forwarding - GetMail 4 Hotmail
Fetchmail
SpamAssassin: Welcome to SpamAssassin
Exchange SpamAssassin Sink
Exchange 2003 Backup and Restore with NTBACKUP
(P.S. I like Entourage, too)