I'm still running my mail server, the same setup I've been using for decades, not because there isn't anything better, but because it mostly works and I don't have to mess with it, there are other things that I spend my time on :)
Postfix, Cyrus IMAP, Spamassasin, Thunderbird on the front end.
The only thing that's changed since last month is that my new internet provider will NOT provide a static IP, so I have to use dynamic dns (I'm using cloudns.net), a bit of a pain, and I obviously can't send email out reliably, so I use google for outbound.
Roberto