I run iRedMail (a collection of dovecot, postfix etc, plus sogo and roundcube web clients and managed by a nice web frontend, all open source and runs on any linux.

I've run for about 8 years, no dramas other than my isp technocally doesnt allow it. But they don't block anything and occasionally they submit their ip ranges for customers to places like spamhaus, so i just script check every month to see if they added my ip back, then i just submit removal, it takes all of 30sec. (IP is semi static, probably changes once every 9 months or so, so not a drama to update dkim on my domain registrar.)