Some time ago a few friends and I rented a root server, each of us maintaining one or more services on it. Since I gathered some experience in the field my part is to maintain the mailserver. This way we have a decentralized mail service at our hand, that is not so easily spied upon.
For running the mailservice I chose the combination of Postfix and Dovecot with SASL managed by Dovecot. To configure everything I really recommend the Dovecot wiki as well as the Postfix documentation. When installing from Debian repositories you get a simple working configuration out of the box.
If you want to learn to do this by yourself, just install these services and tinker with them. Thats the best approach I can recommend, though maybe not the simplest.