Security in OS X
Go here to retrieve the Apple Mac OS X v10.3.x "Panther" Security Configuration Guide by the Systems and Network Attack Center (SNAC) of the U.S. National Security Agency.
Securing Mac OS X: A Corsaire White Paper (pdf).
Apple Security Update 2004-06-07
How to Read .Mac Mail on a SonyEricsson Phone Securely: "I thought it was high time to document how to get .Mac mail over SSL working [...] Of course you can always use .Mac IMAP mail without encryption, but hey, it's your password [...] The following sections detail the basic technique, which should be applicable to just about any secure POP3 or IMAP service (such as Gmail) as well as any oddball WAP/HTTPS sites you may encounter."
Firewall configuration for OS X.3: A good, brief introduction most useful for people who already know the basics about firewalls.