Everything You Need to Know About POP

Post Office Protocol (POP) is an internet standard that makes it possible to download email messages from an email server to a computer. POP has been updated twice since it was first published in 1984 as POP1. Post Office Protocol, Version 2 (POP2) was published in 1985. Post Office Protocol, Version 3 (POP3) was published in 1988; this version includes new mechanisms for authentication and other actions.

Incoming email messages are stored at a POP server until the user logs in (with an email client) and downloads the messages to their computer. The POP standard doesn't include means to send messages. Simple Mail Transfer Protocol (SMTP) is used to send email.

POP and Internet Message Access Protocol (IMAP) are similar in that both are used for email retrieval. However, POP is older and defines only simple commands for email retrieval; IMAP enables synchronization between devices and online access. With POP, messages are stored and managed locally on one computer or device. Therefore, POP is easier to implement and typically more reliable and stable.

POP is a limited protocol that allows an email program to only 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 track which messages have been fetched, sometimes this process fails and messages may be downloaded again. Also, with POP, it's not possible to access the same email account from multiple computers or devices and have actions synchronize between them.