Configuring Sendmail

Sendmail has long been the most common SMTP server. Although its popularity has dropped somewhat in recent years, it remains the dominant mail server on the Internet at large and is the standard mail server installed in many Linux distributions, including Fedora, Red Hat, and Slackware.

To configure sendmail, you must first know where to find its configuration files, understand their formats, and know how to create and modify these files. These tasks are trickier in sendmail than in most other mail servers, which is one of sendmail’s big drawbacks compared to other popular Linux mail servers, especially for new mail administrators. This chapter looks at three particularly important areas of sendmail configuration: address options, relay options, and antispam options.


Sendmail is an extremely complex server, so this chapter can only begin to scratch its surface. If you need to do more with sendmail than is described here, you should consult its own documentation or a book on sendmail, such as O’Reilly’s sendmail or sendmail Cookbook.

Sendmail Configuration Files

The main sendmail configuration file is called , and it’s usually located in /etc, /etc/mail, or some other subdirectory of /etc. Unfortunately, this file is very difficult to edit directly because the configuration options are numerous and have formats that are fairly obtuse. For this reason, few people even attempt to edit this file directly. Instead, they use the m4 utility to create a ...

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