The classic Post Office Protocol (POP) is one of the most commonly used protocols by Internet Service Providers for receiving e-mails. However, it is relatively insecure when it comes to handling passwords
. This disadvantage is eliminated by the APOP protocol (Authenticated Post Office Protocol), an enhanced Post Office Protocol (POP) with improved security mechanisms. The Authenticated Post Office Protocol encrypts the authentication cryptographically to protect it against unauthorized eavesdropping. If the SSL protocol, Secure SocketLayer (SSL), is used, then the APOP protocol is not required.