http://www.rfc-editor.org/rfc/rfc1342.txt
RFC 1342: Representation of Non-ASCII Text in Internet Message Headers, K. Moore1992-06-01T23:00:00-00:00This memo describes an extension to the message format defined in [1] (known to the IETF Mail Extensions Working Group as "RFC 1341"), to allow the representation of character sets other than ASCII in RFC 822 message headers. [STANDARDS-TRACK]