In computing, the Post Office Protocol
(POP) is an application-layer Internet standard protocol used by local e-mail
clients to retrieve e-mail from a remote server over a TCP/IP connection.
POP
and IMAP (Internet Message Access Protocol) are the two most prevalent Internet
standard protocols for e-mail retrieval. Virtually all modern e-mail clients and
servers support both. The POP protocol has been developed through several
versions, with version 3 (POP3) being the current standard. The design of POP
and its procedures supports end-users with temporary Internet connections, such
as dial-up access, allowing these users to retrieve e-mail when connected and
then to view and manipulate the retrieved messages when offline.
Although most
clients have an option to leave mail on server, e-mail clients using POP
generally connect, retrieve all messages, store them on the user' s PC as new
messages, delete them from the server, and then disconnect. In contrast, the
newer, more capable Internet Message Access Protocol (IMAP) supports both
connected (online) and disconnected (offline) modes of operation. E-mail clients
using IMAP generally leave messages on the server until the user explicitly
deletes them. This and other aspects of IMAP operation allow multiple clients to
access the same mailbox. Many e-mail clients support POP as well as IMAP to
retrieve messages; however, fewer Internet Service Providers (ISPs) support
IMAP.
Source: Wikipedia, the free encyclopedia