POP (Post Office Protocol)

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POP Allows Your Email Program to Fetch Electronic Letters. ©Eddy Van 3000; CC BY-SA 2.0 license


POP (Post Office Protocol) is an internet standard that defines an email server and a way to retrieve mail from it.

​The current version is POP3.

How Does POP Work?

Incoming messages are stored at a POP ​ server until the user logs in (using an ​ email client and downloads the messages to their computer.

While SMTP is used to transfer email messages from server to server, POP is used to collect mail with an email client from a server.

How Does POP Compare to IMAP?

POP is the older and much simpler standard. While IMAP allows for synchronization and online access, POP defines simple commands for mail retrieval. Messages are stored and dealt with locally on the computer or device alone.

POP is therefore easier to implement and typically more reliable and stable.

Is POP Also for Sending Mail?

The POP standard defines commands to download emails from a server. It does not include means to send messages. For sending email, SMTP (Simple Mail Transfer Protocol) is used.

Does POP Have Disadvantages?

POP’s virtues are also some of its disadvantages.

POP is a limited protocol that lets your email program do nothing but download messages to the computer or device, with an option to keep a copy on the server for future download.

While POP lets email programs keep track of which messages have been fetched already, sometimes this fails and messages may be downloaded again.

With POP, it is not possible to access the same email account from multiple computers or devices and have actions synchronize between them.

Where Is POP Defined?

The principal document to define POP is RFC (Request for Comments) 1939 from 1996.

(Updated December 2015)

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