The primary reason for this book, the third edition of sendmail, is the release of versions 8.9 through 8.12 of the sendmail program. V8.12 of sendmail, in particular, differs so significantly from earlier versions that a massive rewrite was called for.
Many of you will notice that the tutorials of earlier editions have been replaced with a single introductory chapter in this edition. The tutorials were eliminated because V8.10 sendmail changed to an all m4-based compilation and configuration, and because newer versions of sendmail tend to insulate the administrator from sendmail’s internals. Because sendmail now places much more emphasis on the mc configuration file, it automatically produces 99% of the rules and rule sets you will ever need. Although you will need to write your own rule sets from time to time, the chapters about rule sets should prove sufficient.
You might also notice some new chapters. A chapter on performance tuning has been added because so many sites now seek to make mail delivery efficient. A chapter on handling spam has been added because sendmail V8.10 and above is now rich in antispam features. A chapter describing the other programs supplied with sendmail, such as vacation and makemap, has been added because those additional programs are pivotal to the daily operation of sendmail. Other chapters have been massively expanded because sendmail has added dozens of new features, options, and macros.
This edition of the sendmail book assumes you are using V8.12, the current version of the sendmail program. It follows the same general format as earlier editions of the book, but we realize this might not be the most convenient arrangement for readers who are primarily interested in what has changed since the last edition. To help minimize this problem, we have added Appendix B, in which the many improvements of the intervening versions are categorized by chapter, complete with references to the appropriate sections within this book.
 The Things to Try tutorial sections are also gone because they were too version-specific and impossible to keep current. Instead, configuration solutions and examples are now spread throughout this book.