Episode 6: Sendmail Not Listening to Local Domain but working for other Domain..

There had been changes to the way Sendmail handles email from previous versions. Previously, Sendmail will connect directly to the receiving Mail Transport Agent (MTA). It is possible, at that point, not to run the Sendmail daemon but still be able to send emails. In Red Hat Enterprise Linux 3 and later, Sendmail runs 2 daemons: one to listen on localhost to queue the mail and one to actually send the mail.


In some configurations, Sendmail uses a smart host to relay outgoing emails. For security purposes, it is also sometimes configured not to run as a daemon process. This configuration works fine in Red Hat Enterprise Linux 2.1 but not in Red Hat Enterprise Linux 3 and later. If Sendmail does not listen on the localhost, emails to the local system will be deferred. Below is a sample log of what happens:




Jun 27 11:28:46 localhost sendmail[3272]: j5R1SktO003272: from=root, size=37, class=0, nrcpts=1, msgid=<200506270128.j5R1SktO003272@dhcp-99-example.com>, relay=root@localhost
Jun 27 11:28:46 localhost sendmail[3272]: j5R1SktO003272: to=joe, ctladdr=root (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30037, relay=[127.0.0.1] [127.0.0.1], dsn=4.0.0, stat=Deferred: Connection refused by [127.0.0.1]


Using ps ax | grep sendmail to check if Sendmail is running would give the following output:




3240 ? Ss 0:00 sendmail: Queue runner@01:00:00 for /var/spool/mqueue
3246 ? Ss 0:00 sendmail: Queue runner@01:00:00 for /var/spool/clientmqueue


Solution:

To correct this problem, it is necessary that Sendmail listens on localhost. Make sure that /etc/sysconfig/sendmail is configured with the option:




DAEMON=yes


After making any changes, restart Sendmail by running this command:




service sendmail restart


Verifying with ps ax | grep sendmail should show something similar to this:




2387 ? Ss 4:31 sendmail: accepting connections
2393 ? Ss 0:00 sendmail: Queue runner@01:00:00 for /var/spool/clientmqueue