Sendmail: Theory and Practice, Second Edition
A comprehensive guide to the nooks and crannies of Sendmail, the most-popular electronic mail utility for those using Unix-based servers.
TABLE OF CONTENTS Sendmail: Theory and Practice, Second Edition
Chapter 6: Configuration Basics
The Sendmail configuration file is called sendmail.cf. It tells Sendmail how to parse and rewrite mail addresses, what MTAs it should know about, how to route mail, and to set options and other values. sendmail.cf is designed to be easily parsed by the Sendmail program, and as a result is not optimized for parsing by human brains. Some people find it obtuse and hard to read and understand, but we trust that if you take the time to study Sendmail configuration with our help, after a while you will see that it really is obtuse and hard to read and understand. ("Ha Ha," as Dave Barry would say, "Just kidding.")
6.1. Basic Format, Variables, and Classes
sendmail.cf is best understood if looked at a section at a time. To do that we will explain how to recognize each section and, in the telling, describe that section's purpose or function. We'll also help you understand the configuration file's characters and symbols. (A triple mocha would be a good thing to have in your hand about now.)
sendmail.cf was designed to be easy to parse by Sendmail, at some cost in readability by humans. sendmail.cf is made up of different types of lines, and a line's type is determined by its first character. Blank lines are ignored and should be used whenever they add readability. Lines beginning with a tab (ASCII HT) character are treated as continuations of the previous line.
The other types of
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