Postfix
From John Freier
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