This guide is organized in five phases:

An introduction that parallels the introductory material in the second edition of this book. This phase is intended to give you a general overview of sendmail, its parts, modes, roles, and files.
How to download, build, and install sendmail. If you don't already have the latest version running on your machine, you might have to undertake this step first. This phase steps you through the basic installation.
The meat and potatoes of sendmail are its rules and rule sets. In this phase, we introduce the concept of rules, show how to use them, and provide real-world examples of how to employ them in your own configuration file.
In this phase we first provide an overview of the configuration file, which is central to managing sendmail, then delve down to some of its key components. By the end of this phase you will understand most of the important parts of the configuration file.
To create your own configuration file, you must use the m4 processor. This final phase shows how to use m4 and the steps necessary to create a configuration file using it. We finish with a tour of the many configuration FEATURE( ) commands available.

If you wish to continue after finishing this guide, we recommend you read the chapters in Part II of the book first, then the chapters in Part I.

Section 1.1: Describes the fundamental nature of email
Section 1.3: Describes the difference between an MUA and an MTA and shows how sendmail fits into that picture
Section 1.4: Gives an overview of sendmail, including its various parts and their relationship to the configuration file
Section 1.5: Shows how to run sendmail by hand, and then describes the parts of an email message: the header, body, and envelope
Section 1.6: Illustrates sendmail's roles: in the filesystem; with aliasing; managing the queue; performing local delivery; and delivering over the network
Section 1.7: Shows how to run sendmail, how to kill and restart sendmail, and the various modes of sendmail, such as printing the queue, and rebuilding aliases
Section 1.8: Presents a brief overview of the sendmail configuration file

Section 19.1: Shows how to declare rule sets and how rules fit under each rule set
Section 18.1: Provides an overview of why rules are necessary
Section 18.2: Describes the parts of a rule and how rules act like little if-then clauses
Section 18.3: Describes what tokens are, and how rules are tokenized
Section 18.4: Illustrates the workspace, and how the workspace is processed by rules
Section 7.1: Shows many actual rule sets and describes them in detail

Section 17.1: Provides a total overview of the configuration file
Section 21.3: Describes sendmail macros and how they fit in the configuration file
Section 22.1: Describes class macros and how they fit in the configuration file
Section 23.2: Describes database macros and how they fit in the configuration file
Section 20.1: Describes delivery agents and how they fit in the configuration file
Section 24.3: Describes options and how they fit in the configuration file
Section 11.1: Describes the queue and how the queue fits into the configuration file

Section 4.1: Describes the m4 processor and how to use it
Section 4.2: Presents an overall picture of how to configure with m4
Section 19.1.7: Shows how to insert your own rules and rule sets with m4
Section 20.3: Shows how to declare delivery agents with m4
Section 24.4: Shows how to declare and tune options with m4
Section 4.8: Lists and describes all the FEATURE( ) macros available, and the value and use of each