Rating: 

Sendmail is insecure, sendmail allows open relaying, blah blah blah.

This book was published in March of 2007, anyone keeping abreast of technology knows that open relaying and may other flaws in sendmail have been fixed quite some time ago.

The authors may have a personal preference for postfix, but if anyone is going to write a book and call it something as definitive as "Linux Server Administration", with the caption "Solve Real-Life Linux Problems Quickly" in bold caps across the top of the cover, it had better damn well know and cover sendmail in resonable detail in a way that the average sysadmin can pick up and use quickly. Is it still the dominant MTA worldwide, and there are a lot of sysadmins who are in the position of having to maintain a server that someone else set up, so they do not have the choice, in "Real-Life" of what MTA to use and maintain at least in the short term.

Other than that, the book has proven valuable in many ways, though sometimes the chosen wording is a bit inaccurate (i.e.: p.137: the code snippet is indeed a PHP script, but it is only a CGI program if PHP is being run in CGI mode).