Ars Technica’s Lee Hutchinson has only posted the first installment, but this looks to be a seriously good piece on self-hosting email:
He starts off with a good dose of reality: it’s a lot of work, and when you screw it up you can make your online life really miserable really quick.
If you want to run a Linux mail server, either on your own physical server or a virtual hosted one, start reading. I’m collecting parts for my new server and I expect this to be useful even if I’m running OS X.
If you have never considered running a mail server, I’m not going to try to talk you into it. Maintaining your own for a few users is smaller in resources than a corporate server, but only somewhat smaller in complexity. You might, however, want to read how it works just to understand how email can be so broken.