Post Office Protocol (POP)

Post Office Protocol (POP) is a set of rules used by email applications to get email from an email server. Most Internet Service Providers (ISPs) use POP to provide their subscribers with access to their email.

POP was designed for dial-up users whose Internet connections were intermittent and not reliable. For this reason, POP downloads the entire email message to your computer, so that you don't have to be connected to the Internet to view it. Once the email message is downloaded, it is deleted from the server. The problem with this approach is that you can then no longer access the message from a different computer. If your email is downloaded to a public computer, you may not be able to access it later and it could be viewed by others.

Newer versions of POP do support a “leave mail on server” option, but this feature has some bugs, and not all email clients understand it. Newer versions of POP also support secure, encrypted transmission using SSL, TLS and MD5 hashing.

The alternative to POP is Internet Message Access Protocol (IMAP). Since POP is older than IMAP, it is a much more common and popular email protocol, despite its inferiority to IMAP. Most email clients, such as Microsoft Outlook, Mozilla Thunderbird, and Eudora, support POP.