Supports Postfix as MTA with SMTP

Summary:
    Install and configure Postfix as MTA, on local host with SMTP works
    for outbound emails. 

TestPlan:
    Configured Postfix on Amazon EC2 instance, where Phabricator is running,
    used SMTP, sent some mail to myself and my team.

[TODO] : Write a documentation of how-to
    configure postfix, running as MTA with SMTP.