Summary

One thing we really did not touch on in this chapter is a set of firewall rules you can use to fight spam. This is a topic near and dear to us, as we are sure it is to you. Everyone hates spam, and there are more strategies for fighting spam than you can poke a stick at. We also are in the fight against spam, and you can see our anti-spam efforts at http://www.atomicrocketturtle.com.

Filter rules themselves, we feel, are not a realistic mechanism for dealing with spam; there are too many bad guys coming from too many IPs to realistically create a mechanism in iptables. A better option would be to use one of the RBL (http://www.mail-abuse.com/) services in your MTA itself. Even these services are not a silver bullet in fighting spam, which is why we opt for either content-filtering systems, such as spamassassin (http://www.spamassassin.org), a DSPAM (http://www.nuclearelephant.com/projects/dspam/), or challenge-response systems such as TMDA (http://tmda.net/).

This is a topic that really deserves its own book (or two...or three...).

That being said, this chapter should leave you with a good understanding on how to create host-based firewall rules or DMZs to contain your mail servers. The rules themselves are intended to be self-contained, so you should not have to reference other chapters to get something working on your firewall right away.