TCP/IP Post Office Protocol (POP/POP3)
The overall communication model used for TCP/IP email provides many options to an email user for accessing her electronic mailbox. The most popular access method today is the simple offline access model, in which a client device accesses a server, retrieves mail, and deletes it from the server. POP was designed for quick, simple, and efficient mail access; it is used by millions of people to access billions of email messages every day.
POP Overview, History, Versions, and Standards
Of the three mailbox access paradigms—online, offline, and disconnected—the offline model is probably the least capable in terms of features. And it is also the most popular. This may seem counterintuitive, but it is in fact a pattern ...