An RFC from the IETF, this is part 5 in the MIME standard,

• Full text of RFC 2049 (http://www.ietf.org/rfc/rfc2049.txt) Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples. N. Freed, N. Borenstein. November 1996. (Format: TXT=51207 bytes) (Obsoletes RFC 1521, RFC 1522[?], RFC 1590) (Status: DRAFT STANDARD)