Post Office Protocol (POP): Definition & Overview

Instructor: David Whitsett

David has taught computer applications, computer fundamentals, computer networking, and marketing at the college level. He has a MBA in marketing.

This lesson will define POP, explain a little about how the technology works and how it came about, as well as give some examples of everyday usage. You'll then be able to test your new-found knowledge with a quiz.


If you've ever sent or received an email through the Internet, chances are you have used Post Office Protocol (POP). Post Office Protocol (POP) is an Internet standard (meaning everyone has agreed on how it's structured) protocol for pulling email down from a remote server. We'll break this down into more detail, but to help you visualize this, think about sending a clerk to the mail room to get your mail and he/she brings it back and plops it into your inbox on your desk.

POP is an application layer protocol in the Open Systems Interconnection (OSI) Model. The OSI Model is a theoretical construct used to describe how communications happen across a network. There are 7 layers. The bottom layer, layer 1, is the physical layer; it describes the physical structure data uses to travel across the network, like cabling. Layer 7, the application layer, is the top layer which describes how two applications (think 'programs') talk to each other and this is where POP lives. The current version of POP is the third, or POP3.

So POP is used to help define the conversation (to set the ground rules, if you will) that happens between your device and the remote server somewhere on the Internet that holds your email. Think of your device and the remote server speaking a common language so they can discuss how to get your mail to you. POP is the protocol for pulling your messages down and there's another application layer protocol called Simple Mail Transport Protocol (SMTP) that has rules for sending your messages out. The two protocols work together seamlessly to do the whole job.

POP diagram

History and Evolution

Prior to Internet-based email, email usage was limited because users who wanted to exchange emails had to be on the same network, say within one company or through a common service like America Online (AOL). There were different brands of email server software and they used proprietary protocols to communicate, which often made communication between two companies tricky. The development of open standard protocols for the Internet like POP made email communication through a common network possible.

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