http://www.rfc-editor.org/rfc/rfc0841.txt
RFC 0841: Specification for message format for Computer Based Message Systems, 1983-01-01T23:00:00-00:00This RFC is FIPS 98. The purpose of distributing this document as an RFC is to make it easily accessible to the ARPA research community. This RFC does not specify a standard for the ARPA Internet. Obsoletes RFC 806.