Does your ISP prohibit email message attachments larger than 10 MB or impose other restrictions that you find cumbersome? Your Linux system can provide an email server that isn’t subject to such arbitrary restrictions.

The sendmail package is a powerful Mail Transfer Agent (MTA), which transfers email from one system to another.

Depending on the options you selected during system installation, sendmail may already reside on your system. To check whether it’s installed, issue the command:

            rpm -q sendmail

If sendmail is installed, the command reports its version number; otherwise, the command reports that sendmail is not installed.

To install sendmail, use GnoRPM to install the sendmail, sendmail-cf, and m4 packages.

sendmailstarts automatically when you install it; to check the status of sendmail, issue the following command:

            service sendmail status

The command should identify the process ID of sendmail. If sendmail is not running, you can start it by issuing the following command:

            service sendmail start

You can stop sendmailby issuing the command:

            service sendmail stop

You probably won’t need to change sendmail’s hugely complex configuration file, /etc/sendmail.cf. However, if you do, you can restart sendmail by issuing the command:

            service sendmail restart

If you want sendmailto start automatically when your system boots, issue the command:

            chkconfig --level 345 sendmail on

You can also use Linuxconfto configure sendmailto start automatically.

You should now be able to send and receive email. Test your server by sending yourself an email message:

[root@localhost /etc]# mail 
            [email protected] 
Subject: test message
            This is a test.
            .
Cc: 
[root@localhost /etc]#

Once you know that the server is working, you can configure your favorite mail client to specify your own system as your mail server. For example, if you’re using Netscape Navigator, select Edit → Preferences → Mail Servers. Make a note of the existing mail server settings, just in case something goes wrong. Then, change the incoming and outgoing mail server options to specify your Linux machine.

The sendmail service is capable of sending and receiving email. If you plan to receive email, your system should be continuously connected to the Internet. This means that you’ll need a static IP address and a registered domain name. And, as explained earlier, you should also have an understanding ISP. Contact your ISP prior to setting up any web or mail server of your own.

By default, sendmail accepts connections only from the local host. To configure sendmail to accept connections from other hosts, you must edit the /etc/mail/sendmail.mc file. Insert a hash mark (#) in column one of the line containing the term DAEMON_OPTIONS and the line containing FEATURE(accept_unresolvable_domains) and then save the file. Then, issue the following commands:

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