Chapter 21. Mail Transport Agent (MTA) Configuration

A Mail Transport Agent (MTA) is essential for sending email from a Red Hat Linux system. The Mail User Agent (MUA) such as Mozilla Mail, Mutt, Pine, and Evolution is used to read and compose email. When a user sends an email from an MUA, the messages are handed off to the MTA, which sends the message to a series of MTAs until it reaches its destination.

Even if a user does not plan to send email from the system, some automated tasks or system programs might use the /bin/mail command to send email containing log messages to the root user of the local system.

Red Hat Linux 8.0 provides two MTAs: Sendmail and Postfix. If both are installed, sendmail is the default MTA. Mail Transport Agent Switcher allows a user to select either sendmail or postfix as the default MTA for the system.

To start the Mail Transport Agent Switcher, select Main Menu Button (on the Panel) => Extras => System Settings => Mail Transport Agent Switcher, or type the command redhat-switchmail at a shell prompt (for example, in an XTerm or GNOME terminal).

The program automatically detect if the X Window System is running. If it is running, the program starts in graphical mode as shown in Figure 21-1. If X is not detected, it starts in text-mode. To force Mail Transport Agent Switcher to run in text-mode, use the command redhat-switchmail-nox.

If you selected Postfix, you must make sure the sendmail service is stopped and the postfix service is started:

/sbin/service sendmail stop
/sbin/service postfix start

If you selected Sendmail, you must make sure the postfix service is stopped and the sendmail service is started:

/sbin/service postfix stop
/sbin/service sendmail start

To enable or disable the services at boot time, you must configure the runlevel with Services Configuration Tool, ntsysv, or chkconfig. Refer to Chapter 13 for details.

For more information about email protocols and MTAs, refer to the Official Red Hat Linux Reference Guide.