In some releases of Red Hat Enterprise Linux 5, the sendmail Mail Transport Agent (MTA) accepted network connections from external hosts by default. In Red Hat Enterprise Linux 6, sendmail by default only accepts connections from the local system (localhost). To grant sendmail the ability to act as a server for remote hosts, perform one of the following steps:
Edit /etc/mail/sendmail.mc and change the DAEMON_OPTIONS line to also listen on network devices
Comment out the DAEMON_OPTIONS line in /etc/mail/sendmail.mc. Then install the sendmail-cf package and regenerate /etc/mail/sendmail.cf by running the following commands:
su -c 'yum install sendmail-cf'
su -c 'make -C /etc/mail'
