Cold Mailing Glossary letter p

POP (Post Office Protocol)

Post Office Protocol is one of the primary methods of retrieving messages from your email server and delivering them to your email software.

If you want the heavy maths and science, POP uses the TCP/IP protocol stack for the network connection and SMTP (Simple Mail Transfer Protocol) for end-to-end email communication.

However, it’s much easier to understand if we put it like this: POP gets new messages from the remote server, and SMTP sends your emails to it.

How POP works

Your new emails are stored on a remote server. The email software on your device (Mac, PC, phone, tablet…) talks to the server and downloads all the new messages so you can read them.

Depending on how you set up your device software, the messages will either remain on the server indefinitely, for a specified length of time or deleted straight away. Usually, they get deleted.

POP isn’t made to send messages; that’s why your devices need SMTP to take care of that part of the process.


IMAP (Internet Message Access Protocol) is a similar system, also designed to retrieve new emails from your remote server. POP is the more basic of the systems, with current trends showing IMAP to be slowly replacing it, becoming the most popular and the preferable option for many ESPs.
What IMAP does differently to POP is that it synchronizes each of your email packages to mirror what’s on the server. So, if you delete half a dozen messages on your phone, they disappear from your PC too. IMAP saves the user time by not having to carry out the same updates on several machines and devices.
In a nutshell, POP typically removes messages from the server to your computer or device, whereas IMAP stores them on the server and downloads a local copy for you to read and reply to.

The history of POP

Sadly, this is nothing to do with music culture or the many bands and artists that contributed to popular music over the past fifty or sixty years.
Post Office Protocol was first introduced in 1984 with, yes, you guessed it, its first version: POP1. It was published in a Request for Comments (as RFC 918) by the Internet Engineering Task Force, designed as a simple method of mail retrieval from a server. The idea was purely to take advantage of being able to read messages offline, as opposed to continually accessing the server online.

POP2 followed only a year after in 1985, and the current version in use today, POP3, in 1988.

POP3 has been revised several times since its arrival, but still operates on its original simple principles.