Postfix is a free open source mail transfer agent (MTA). It is easy to administer, fast and as well as the secure MTA. It’s an alternative to Sendmail, which is the default MTA for RHEL.

Well, let us see how to setup a basic local mail server using Postfix, Dovecot and Squirrelmail On CentOS 6.5 [or Opensuse], although it should work on RHEL, Scientific Linux 6.x series [or SLES Servers].

Full articles here, from Unixmen:
Setup Local Mail Server Using Postfix, Dovecot And Squirrelmail On CentOS 6.5/6.4
Setup Local Mail Server Using Postfix, Dovecot And Squirrelmail On OpenSUSE 13.x