Chapter 1. Introduction

There is a considerable amount of information available in print and on the Internet on the topic of configuring electronic mail systems running sendmail, but comparatively little information on how to tune these systems to handle anything except the most nominal amount of email traffic. Of course, as the most straightforward installation of sendmail and a Post Office Protocol (POP) daemon under UNIX on a commodity desktop box can easily accommodate more than 1,000 individual users and handle more than 100,000 modestly sized email messages per day, at many sites performance tuning of these systems isn't critical. Nonetheless, as email rapidly becomes the preferred method for much of the communication that occurs in the world today, more and more systems are feeling the strain. For tuning tips, one can glean some well-known tricks by scouring old Usenet news postings and mailing list archives, but these methods have not been widely disseminated, much less gathered together in a single document. Even so, this book contains many suggestions that, I believe, have been documented for the first time.

This book focuses on solutions based on sendmail, but also references other UNIX-based Open Source email software packages. Much of the information in this document is applicable to email systems not based on sendmail or, for that matter, non Open Source or non UNIX-based systems.

This book does not try to answer all possible questions about running electronic mail systems. For example, aside from a brief introduction to the Open Source sendmail package in Chapter 2, it does not discuss changing the logical behavior of one's sendmail-based email system. Instead the focus is entirely on making a single email server perform its duties more efficiently. If the reader is interested in reducing spam, filtering email, or making any number of other configuration changes, many good sources for this sort of information [SEN] [SG98] exist; however, this book is not one of them. Further, the topic of increasing capacity by running email as a distributed system is not considered here in depth. Instead, this book focuses on tuning individual machines to perform their email-related tasks better. For information on building a distributed email system, the reader may want to consider other sources [CBB97] [SHB⁺98].