E-mail, specifically the Simple Mail Transport Protocol (SMTP), is one of the oldest protocols on the Internet. Even after all this time, it is still heavily utilized by most businesses out there. While these days hosted e-mail infrastructure like hosted Exchange or Google apps is quite common, but it's still a good idea to understand what is occurring under the cover. In this chapter, you'll set up your own e-mail infrastructure, which is able to send and receive mail over the public internet. We'll also learn some basic methods for dealing with the problem of unsolicited commercial e-mail (spam).
There are a few core pieces to e-mail infrastructure:
Mail Transfer Agent (MTA): The MTA is responsible for receiving an e-mail message from the network or from local processes, determining if it should be accepted or rejected, and then pass it either on to the next MTA or hand off the message to an MDA for delivery. A few common examples of MTAs for Linux are Sendmail, Postfix, or...
