Common Sendmail Configuration Changes

When altering the Sendmail configuration file, it is best not to edit an existing file, but to generate an entirely new /etc/mail/sendmail.cf file.

Before changing the sendmail.cf file, it is a good idea to create a backup copy.

To add the desired functionality to Sendmail, edit the /etc/mail/sendmail.mc file as the root user. When finished, use the m4 macro processor to generate a new sendmail.cf by executing the following command:

m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

By default, the m4 macro processor is installed with Sendmail but is part of the m4 package.

After creating a new /etc/mail/sendmail.cf file, restart Sendmail for the changes to take effect. The easiest way to do this is to type the following command:

service sendmail restart

The default sendmail.cf file does not allow Sendmail to accept network connections from any host other than the local computer. To configure Sendmail as a server for other clients, edit the /etc/mail/sendmail.mc file, and either change the address specified in the Addr= option of the DAEMON_OPTIONS directive from 127.0.0.1 to the IP address of an active network device or comment out the DAEMON_OPTIONS directive all together by placing dnl at the beginning of the line. When finished, regenerate /etc/mail/sendmail.cf by executing the following command:

m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

The default configuration which ships with Community Enterprise Linux works for most SMTP-only sites. However, it does not work for UUCP (UNIX to UNIX Copy) sites. If using UUCP mail transfers, the /etc/mail/sendmail.mc file must be reconfigured and a new /etc/mail/sendmail.cf must be generated.

Consult the /usr/share/sendmail-cf/README file before editing any files in the directories under the /usr/share/sendmail-cf directory, as they can affect the future configuration of /etc/mail/sendmail.cf files.