Describes the widely implemented Simple Mail Transfer Protocol (SMTP) designed to transfer mail reliably and efficiently and relay mail across transport service environments. Obsoletes RFC 821, 974, 1869.

Describes the widely implemented Post Office Protocol (POP), which allows a client to retrieve mail that a server is holding for it.

Describes the Enhanced Mail System Status Codes, a set of status codes for reporting mail system errors and delivery status notifications.

Describes the Internet Message Access Protocol (IMAP), which allows a client to access and manipulate electronic mail messages on a server, and permits manipulation of remote message folders.

Describes the Local Mail Transfer Protocol (LMTP), for transporting mail into a system where a mail receiver does not manage a queue.

Defines a portion of the Management Information Base (MIB) for use with network management protocols, and extends the basic Network Services Monitoring MIB to allow monitoring of Message Transfer Agents (MTAs).