10.9 Summary

sendmail sends and receives SMTP mail, processes mail aliases, and interfaces between user mail agents and mail delivery agents. sendmail is started as a daemon at boot time to process incoming SMTP mail. sendmail aliases are defined in the /etc/aliases file. The rules for interfacing between user agents and mail delivery agents can be complex. sendmail uses the sendmail.cf file to define these rules.

Configuring the sendmail.cf file is the most difficult part of setting up a sendmail server. The file uses a very terse command syntax that is hard to read. Sample sendmail.cf files are available to simplify this task. Most systems come with a sample file and others are available with the sendmail V8 software distribution. The sendmail V.8 sample files must first be processed by the m4 macro processor. Once the proper sample file is available very little of it needs to be changed. Almost all of the changes needed to complete the configuration occur at the beginning of the file and are used to define information about the local system, such as the hostname and the name of the mail relay host. sendmail provides an interactive testing tool that is used to check the configuration before it is installed.

This chapter concludes our study of TCP/IP servers configuration, our last configuration task. In the next chapter we begin to look at the ongoing tasks that are part of running a network once it has been installed and configured. We begin this discussion with troubleshooting.