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
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 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 panel) => =>
=> , 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.
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.
