In this chapter we show you how to obtain the latest version of sendmail in source form, then how to tune, build, and install it yourself. Although this process can be simple, many decisions that can complicate it must be made ahead of time (including the decision of whether or not to use sendmail in the first place).
The sendmail program is not the only MTA on the block. Others have existed for some time, and new MTAs appear on the scene every once in a while. We describe a few of the major MTAs and contrast them to sendmail in the following list: 
 A new arrival on the MTA scene is qmail. It is so new that we did not have time to review it for this edition.
One difference between Smail3.x and sendmail lies in their differing philosophies for parsing addresses. The Smail3.x authors feel that Internet and UUCP addresses are sufficiently standardized that all parsing can be handled by code rather than by configuration rules. If you suspect that Smail3.x may be better for your particular needs, you can get source and documentation from uunet. Look for a file named something like smail-3.*.tar.Z.
More modular than sendmail, zmailer was written by Rayan Zachariassen at a time when sendmail appeared to have been abandoned. Zmailer is modularized by role, with well-defined roles. All decisions are made in configuration files; none are made in code. It tends to be slower than sendmail, but some claim that it is easier to understand. For additional information, contact:
A commercial offering (new and not widely ported). For those who absolutely need commercial support, this may be the answer. It features configuration via email and http forms. Similar to Zmailer, it is modular, each module playing a well defined role. For additional information, contact:
Many other MTAs exist, some good and some not so good. We mention only three here because, after all, this is a book about sendmail.