POP, the Post Office Protocol, is a simple protocol for downloading e-mail from a server. It is typically used through an e-mail client like Thunderbird or Outlook. You can reread the first few sections of Chapter 13 if you want the big picture of where e-mail clients and protocols like POP fit into the history of Internet e-mail.
If you are tempted to use POP, then you should consider using IMAP instead; Chapter 15 will explain the features that IMAP provides that make it a far more solid foundation for remote e-mail access than the primitive operations supported by POP.
The most common implementation of POP is version 3, commonly ...