If you are anything like me you would rather not have anything to do with Sendmail or Postfix, however unfortunately it can be required learning in some circles. That being said this is my second postfix post in what I call my “Postfix: Nasty!” series. The first one can be read here, and  I will be the first to admit that its not very good. However I chock this up to the fact that I really don’t know much about Postfix at all and I’m writing these posts as part of the process of figuring out how to do what with Postfix.

Specifically this post outlines and defines the standard roles that a postfix server can serve. Below are three common roles and their characteristics. You should get to know each of these and how to configure them.

Null Client:

• Only runs Postfix as a local MTA (mail transfer agent… think sendmail and postfix) for the purpose of forwarding to a centralized mail server
• Does not accept local delivery

Inbound-Only Mail Server:

• Handles all inbound mail for a site
• Passes inbound email to an MDA (mail delivery agent) such as Dovecot or Procmail
• Forwards outbound mail to a centralized mail server, just like a Null Client Does

Outbound Mail Relay:

• Also called a Smarthost
• Accepts outbound messages
• Should be configured to forward mail for authorized clients only. Avoid being an Open Relay