Chapter 18. Sendmail

Table of Contents
Introduction to sendmail
Installing sendmail
Overview of Configuration Files
The and Files
Generating the File
Interpreting and Writing Rewrite Rules
Configuring sendmail Options
Some Useful sendmail Configurations
Testing Your Configuration
Running sendmail
Tips and Tricks

Introduction to sendmail

It's been said that you aren't a real Unix system administrator until you've edited a file. It's also been said that you're crazy if you've attempted to do so twice.

sendmail is an incredibly powerful mail program. It's also incredibly difficult to learn and understand. Any program whose definitive reference (sendmail, by Bryan Costales and Eric Allman, published by O'Reilly) is 1,050 pages long scares most people off. Information on the sendmail reference is contained in the bibliography at the end of this book.

Fortunately, new versions of sendmail are different. You no longer need to directly edit the cryptic file; the new version provides a configuration utility that will create the file for you based on much simpler macro files. You do not need to understand the complex syntax of the file; the macro files don't require you to. Instead, you need only list items, such as the name of features you wish to include in your configuration, and specify some of the parameters that determine how that feature operates. A traditional Unix utility called m4 then takes your macro configuration data and mixes it with the data it reads from template files containing the actual syntax, to produce your file.

In this chapter we introduce sendmail and describe how to install, configure and test it, using the Virtual Brewery as an example. If the information presented here helps make the task of configuring sendmail less daunting for you, we hope you'll gain the confidence to tackle more complex configurations on your own.