Standards that guide the development of the Internet are
referred to as Request for Comments (RFC). To allow POP3 clients to
connect, authenticate, and complete other client/server
interactions, Exchange complies with the following RFC
guidelines:
RFC 1939. This RFC defines POP3 and describes its
functionality.
RFC 1734. This RFC defines the optional POP3
authentication command. It states that an authentication mechanism
must be used to access a server and that a protection mechanism
must be used for subsequent transactions.