We began previous editions of this book with a very long tutorial aimed at those new to sendmail. In this edition, however, much of that tutorial has been folded into the chapters that follow, and we present, instead, a brief introductory chapter intended to get new people started. It begins with a look at some of the basic concepts of email and the sendmail program. We will show you sendmail’s basic parts, explore the three parts of an email message, then demonstrate how to run sendmail by hand. We finish with an overview of the roles sendmail plays and of its various modes, and lastly, we take a preliminary look at its configuration file.