Always is the same: the best option is the best for you needs. So, the
best could be any distro that you feel comfortable with. Obviously
there're out there some distros which are server-oriented (CentOS,
Debian) or desktop-oriented and so on, but really it doesn't matter.
Choose your favorite one and do your job.
The main important thing it's not the underlaying SO, it's to understand
and master the smptd (Postfix) and popd/imapd (Dovecot).
Personally I prefer BSD systems.
--
I must not fear. Fear is the mind-killer. Fear is the little-death that
brings total obliteration. I will face my fear. I will permit it to pass
over me and through me. And when it has gone past I will turn the inner
eye to see its path. Where the fear has gone there will be nothing. Only
I will remain.
Bene Gesserit Litany Against Fear.
