Chapter 39. Mail Transport Agent (MTA) Configuration
A Mail Transport Agent (MTA) is essential for
sending email. A Mail User
Agent (MUA) such as Evolution,
Mozilla Mail, Thunderbird, and
Mutt, is used to read and compose email. When a
user sends an email from an MUA, the message is handed off to the MTA,
which sends the message through a series of MTAs until it reaches its
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
Red Hat Enterprise Linux 4 provides three MTAs: Sendmail, Postfix, and Exim. If all three are
installed, sendmail is the default MTA. The
Mail Transport Agent Switcher allows for the selection of
either sendmail, postfix, or exim as the
default MTA for the system.
The system-switch-mail RPM package must be installed to
use the text-based version of the
Mail Transport Agent Switcher program. If you want to use the
graphical version, the system-switch-mail-gnome package
must also be installed.
For more information on installing RPM packages,
refer to Part III Package Management.
To start the Mail Transport Agent Switcher, select
(the main menu on the
, or type the command
system-switch-mail at a shell prompt (for example, in an
XTerm or GNOME terminal).
The program automatically detects if the X Window System is running. If it
is running, the program starts in graphical mode as shown in Figure 39-1. If X is not detected, it starts in
text-mode. To force Mail Transport Agent Switcher to run in
text-mode, use the command system-switch-mail-nox.
Figure 39-1. Mail Transport Agent Switcher
If you select OK to change the MTA, the selected
mail daemon is enabled to start at boot time, and the unselected mail
daemons are disabled so that they do not start at boot time. The selected
mail daemon is started, and any other mail daemon is stopped; thus making
the changes take place immediately.
For more information about email protocols and MTAs, refer to the
Red Hat Enterprise Linux Reference Guide.