I just added SPF support for mail here at technomagik.net!

In case you haven't heard of it, SPF, aka Sender Policy Framework is an innovative anti-spam technology that's very easy to implement. All you need to do is add a couple of DNS TXT records to your domain, to "authorize" valid mail senders. (SPF has a wizard that can generate the relevant records that takes at most a minute to fill out)

If you use the -all option, you can eliminate "joe jobs" against servers that use SPF, and widespread adoption will help combat spam by protecting the envelope sender. The SPF FAQ does a better job explaining all this, you can read it here.

To be truthful, there's more to the story (involving IETF standards, patents, and Microsoft), but I won't get into that. If you want, you can read this undeadly.org article.