Setting up your own mail system is not as simple as it could be, particularly if you want to run it on a box which is used for general computer work. If you have a spare PC lurking around, which you don't mind turning into a really useful server, comsider putting e-smith (
http://www.e-smith.org/) on it. E-smith is a customized Red Hat Linux distribution optimized for ultra-simple installation as a server and gateway. It has SMB file sharing, web serving, virtual hosts and DNS, dial-on-demand, firewalling and masquerading, POP/IMAP/SMTP and Web email etc. etc. All with an easy and flexible web-interface for setting up and customizing.
Best of all for you, it is set up to work with yi.org "out of the box".
I have recently been evaluating their most recent release-candidate for version 4.1 of e-smith and I find it quite the most simple and honestly useful OS install I have ever done.
Check it out!