Definition: APOP, acronym of "Authenticated Post Office Protocol" is an extension of the Post Office Protocol (POP) in which the password is sent in encrypted form.
With standard POP, your user name and password are sent in plain text over the network when you check for mail and can be intercepted by a malicious third party. APOP uses a shared secret that is never exchanged directly but only in an encrypted form derived from a string unique to every log-in process.
Also Known As: Authenticated Post Office Protocol
