Bryan Costales with Eric Allman
sendmail, 2d ed.
O'Reilly & Associates, 1997. ISBN 1-56592-222-0, Pp. 996. $39.95.

Reviewed by Steve Hanson
<shanson@htc.honeywell.com>

Many of the O'Reilly system administration books have been published in multiple editions. Normally, the new editions of these books provide minor updates to keep sysadmins up to date on the latest technologies. The second edition of sendmail is a major rewrite, and the new edition is a necessary addition to the bookshelves of any system administrator who deals with sendmail-based email systems. The original version of sendmail (the bat book) quickly became the standard reference for understanding the intricacies of this often confusing program, and three years later the second edition provides the latest information for the current sendmail 8.8 releases.

Some information has been dropped from the new edition, notably the sections detailing the configuration of versions of sendmail previous to version 8 and other offshoots such as IDA and KJS sendmail. Most manufacturers have updated their sendmail systems to version 8, and if you are blessed with a system running an older version, you're probably better off updating than understanding how to configure an old release.

What is new in this edition is much more detailed information on using the m4 configuration system in sendmail 8. Use of the m4 configurations allows admins to build the complex sendmail.cf file from simple m4 files, which are much easier to understand. Personally, I haven't written a sendmail configuration from scratch since I started using IDA sendmail and its m4 system quite a few years ago. Almost any sendmail configuration can be built using only the m4 configurations. The new configuration information is covered throughout the second edition while different sendmail concepts are discussed. This is a big improvement over the last edition, which spent many chapters describing the details of sendmail.cf rules while relegating the information on m4 files to an appendix.

The second edition also provides detailed information on a number of other topics that were given short shrift in the first edition. The newer book carefully explains the use of the -bt options for sendmail rule testing. It also provides information on the often bewildering enhancements that Sun has made in its own versions of sendmail, including the recent Sun sendmail releases that will support both the old (version 5) sendmail config rules that Sun had supported in the past, and the new modified 8.7 sendmail configuration rules that are allowed in Solaris 2.5 and later. Additional coverage is given to the use of Berkeley DB databases in sendmail configurations as well.

The final, and perhaps most timely, improvement in the second edition is the inclusion of much more information on the checkcompat routine in sendmail. Although checkcompat has existed in sendmail since version 3, the utility of the routine has been unclear in most documentation. In the last few months the amount of spam mail on the Internet has increased at an amazing rate, and an understanding of the creative use of checkcompat will allow your site to filter out email from offending sites, among other uses. So if you can't handle one more irate user coming into your office begging you to fend off the latest get-rich-quick scheme to float in over the wire, read the new checkcompat chapter in this book.

In general, this update to the much beloved bat book cleans out some of the outdated older information in the first edition while expanding on the information presented for sendmail 8, and adding even more information on the latest version 8.8 releases. Even if you have the original sendmail book, the new updated version is worth purchasing.