Which is the official email RFC?

Question

Which is the current official standard that defines valid email addresses?

Wikipedia says there are two RFCs (5321 and 5322), but also an "extension" (RFC 6531), that (confusingly enough) is marked as "Proposed standard" (so it seems "unofficial", or at least not yet approved).

This site (which seems trustable), says that the official RFC is 5321.

Thanks in advance.

Answer 1

SMTP is 5321 and defines the transfer protocol. 5322 defines the data format of email -- what you are allowed to pass in as DATA in SMTP -- including the address format in the headers. The concept of a mailbox is introduced in 5321 but the detailed syntax is deferred to 5322.

Nominally, 6531 itself states that the extension does not modify or amend the base specification. It codifies a mechanism whereby compliant implementations can negotiate additional features by mutual agreement. In practice, though, it enables syntax which is outside the scope of the 5322 specification.

A "proposed standard" is a specification which is a candidate to become an official IETF standard, but many RFCs never get past this stage. That does not make them less official or trusted. See http://en.wikipedia.org/wiki/Internet_Standard for an overview of the process.