Exchange is the best, obviously, but a bit price and needs a lot of server horsepower. Otherwise, you should be able to find a reasonable POP server on the cheap. Check out
Tucows for a list of POP mail servers.
If you want to spend the cash, I highly recommend IMail, but it's expensive. FTGate was OK, MDaemon is a bit better, SLMail is well thought of, as well. Most will run quite nicely on Win2K and will support a variety of Internet mail routing as well.
Also, check
Eudora WorldMail - It's reasonably priced and has some great features which are missing from most shareware products.
- G