[CentOS] Postfix setup

Dear All
I am planning to setup mail server for my domain.

Which one is preferred postfix or sendmail.


I came across a link *
http://ostechnix.wordpress.com/2013/02/08/setup-mail-server-using-postfixdovecotsquirrelmail-in-centosrhelscientific-linux-6-3-step-by-step/
* for postfix mail setup.

It says,
Prerequisites:

   - The mail server should contain a valid MX record in the DNS server.
   Navigate to this link how to setup DNS
server<http://ostechnix.wordpress.com/2013/01/25/setup-dns-server-step-by-step-in-centos-6-3-rhel-6-3-scientific-linux-6-3-3/>
   .
   - Firewall and SELinux should be disabled.


I have disabled iptables as my m/c is behind the firewall.

It says I need to disable firewall. Is it really required. Kindly let me
know.

Best Regards
Austin