Introduction
Postfix is the default Mail Transfer Agent (MTA) for Ubuntu. It is in Ubuntu’s main repository, which means that it receives security updates. This guide explains how to install and configure postfix and set it up as an SMTP server using a secure connection.
What is a Mail Transfer Agent
In other words, it’s a mail server not a mail client like Thunderbird, Evolution, Outlook, Eudora, or a web-based email service like Yahoo, GMail, Hotmail, Earthlink, Comcast, SBCGlobal.net, ATT.net etc…. If you worked for a company named Acme and owned acme.com, you could provide your employees with email addresses @acme.com. Employees could send and receive email through your computer, but not without your computer running all the time. If all your email addresses are at a domain (@gmail.com, @yahoo.com) you do not own (you don’t own Google) or do not host (acme.com) then you do not need this at all.