A collection of useful links.

The Netfilter/Iptables Project - http://www.netfilter.org/

Linuxguruz Iptables Tutorial - http://www.linuxguruz.com/iptables/howto/iptables-HOWTO.html

Qmailrocks.org - My qmail installation guide

Djbdnsrocks.org - My djbdns installation guide