This document defines a profile of the Simple Authentication and Security Layer (SASL) for the Post Office Protocol (POP3). This extension allows a POP3 client to indicate an authentication mechanism to the server, perform an authentication protocol exchange, and optionally negotiate a security layer for subsequent protocol interactions during this session. This document seeks to consolidate the information related to POP3 AUTH into a single document. To this end, this document obsoletes and replaces RFC 1734, and updates the information contained in Section 6.3 of RFC 2449. [STANDARDS-TRACK]