What Is POP3?

Date First Published: 23rd March 2022

Topic: Computer Networking

Subtopic: Internet Protocols

Article Type: Computer Terms & Definitions

Difficulty Level: 5/10

Learn more about what POP3 is in this article.

Short for Post Office Protocol 3, POP3 is an application-layer protocol used for receiving email messages. It is not used for sending messages POP3 works by establishing a TCP connection with the server host, downloading the email message to the device over the internet, and then deleting the message from the server. This process can save a lot of storage space on servers, but it is impossible for email messages to be synchronised across multiple devices, meaning that any modifications made to email applications, such as messages being moved to a different folder will not show up on other devices.

POP3 will work as long as the email application is configured to work with POP3. Each POP3 server has a different address that must be entered in order for it to make a connection with the protocol. In addition, it is necessary for users to enter their username and password in order to successfully receive email through POP3. The secure version of POP3 uses port 995.

Note:

It is called 'Post Office Protocol' as it works in a similar way to mail in a post office that is waiting to be delivered to its final destination. Instead of real mail and letters, POP3 delivers the messages electronically and then deletes them from the server.

Note:

The '3' in POP3 is the version. Version 3 is most commonly used now.

Security

POP3 is an older email protocol than IMAP. Similar to other protocols, POP3 itself is insecure because the data is sent in plain text and could be read by someone monitoring the connection. A secure version of POP3 exists, called POP3S. It stands for Post Office Protocol Secure and it encrypts text into random characters (ciphertext) through SSL/TLS so that it cannot be read by other people if intercepted.

Versions

The first version of POP was called POP1 and it was released in 1984 and specified in RFC 918. POP2 was released in 1985 and specified in RFC 937. As of now, POP3 is the most commonly used version. It was released in 1988 and specified as RFC 1081. The most recent specification is RFC 1939. It was released with an added extension mechanism as RFC 2249 and RFC 1734 as an authentication mechanism.

POP4 is unused. It is an unofficial proposal that adds basic folder management, multipart message support and message flag management. The development of POP4 has not been worked on since 2003.

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