Csoft.net! (Score 2, Insightful)

Check out csoft.net (who used to advertise here on Slashdot back in '95). They are completely focused on reliability (e-mail is hosted/replicated on multiple servers), Unix-friendly, and they sponsor a number of open-source projects as well. They use the Postfix MTA along with a local delivery agent called mailprocd , which provides you with a persistent SpamAssassin process under your own UID.