Postfix

Install Postfix

yum install postfix

Configure Postfix Edit the /etc/postfix/main.cf and make the following changes.

mydomain = example.com
myorigin = $mydomain
inet_interfaces = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
mynetworks_style = host

Start the service

/etc/init.d/postfix start

Add a port to Postfix to listen on. Open /etc/postfix/master.cf and add the following line:

587 inet n - n - - smtpd

Make sure to test and see if relay is denied from an outside connection!