Programming Internet Email

Internet Email Standards

Within the Internet, everything is tried, some of it works, and those that survive long enough without being superceded become standards. Some elements of the Internet mail system have become standards, and some have not. In any case, the Internet is always in motion, so at any time the Internet mail system as a whole consists of many parts that are not strictly standard but are very widely used.

The hierarchy of Internet standards looks like this:

Standards

Protocols adopted as standard for the Internet by the Internet Engineering Steering Group (IESG). Standards have STD numbers, as listed in RFC 1311.

Draft standards

Protocols that are being considered by the IESG as possible standards. Substantial and widespread testing and comments are desired.

Proposed standards

Proposals that the IESG may consider for standardization. Revision of specifications is likely while testing occurs.

Experimental protocols

Protocols that should only be implemented by those participating in a coordinated experiment.

Documented Internet protocols may also be classified as Informational (published for convenience) or Historic (superceded or uninteresting).

Standards are also given a status: “required,” “recommended,” “elective,” “limited use,” or “not recommended.” A host or gateway connected to the Internet must implement required standards and should implement recommended ones. If a host or gateway offers a service covered by an elective standard, it should follow that standard.

The parts ...