Mail is half done on any *nix setup, since sendmail is already there and running, all you need is a pop server to handle incoming mail and you're in business.
I use Virtualmail POP3D and Sendmail for my setup, on FreeBSD.
It's not terribly complicated or flashy, simple pop and smtp server that can handle mail either by true unix user accounts or virtual users via aliases.
http://www.reedmedia.net/software/virtualmail-pop3d/
http://www.sendmail.org/faq/
Why pay for Windows when you can have a more stable setup with only the expense of a day's time reading the manual(s)

.