NATO STANAG 4774 (Confidentiality Metadata Labels) and STANAG 4778 (Metadata Binding) 4778.2-3: Bind labels to email with the Binding-Data header (SMTP profile)

Chapter 3 (urn:nato:stanag:4778:profile:smtp, version 1:2): an internet mail message carries a detached BDO whose MetadataBinding includes a DataReference with a null URI (meaning the whole message) and a mandatory contentType of message/rfc822. The BDO travels in a new Binding-Data header field of key and value parameters following the stated ABNF: the binding-data-object parameter, always present, holds the base64-encoded BDO as a quoted string (split across multiple parameters where line length requires), the binding-type parameter, always present, is a URI naming the profile, and an optional marking parameter carries a language-tagged human-readable marking. Cryptographic protection follows the cryptographic artefact profile.