Linux Administration Cookbook

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Postfix is a Mail Transport Agent (MTA). 

Sadly, this isn't a book on configuring mail servers, because there are many, many books on this subject already. All you need to be aware of is how to interact with a default Postfix installation, should you ever come across one in the wild.

If you want to know more about Postfix, or want to run your own mail server, I would advise against it. However, if you came back and said you really, really wanted to run your own mail server, I would suggest sitting down with Postfix for a weekend, reading up on best practices (don't create an open-relay, for example), and trying not to give up immediately. All power to you. 

Really, though, most companies these days either use some form of ...