http://www.rfc-editor.org/rfc/rfc2311.txt
RFC 2311: S/MIME Version 2 Message Specification, S. Dusse, P. Hoffman, B. Ramsdell, L. Lundblade, L. Repka1998-03-01T23:00:00-00:00This document describes a protocol for adding cryptographic signature and encryption services to MIME data. This memo provides information for the Internet community. It does not specify an Internet standard of any kind.