usefor-article-06 November 2001

5.3.  Message-ID

   The Message-ID header contains the article's message identifier, a
   unique identifier distinguishing the article from every other
   article. The content syntax makes use of syntax defined in [RFC
   2822], subject to the following revised definition of no-fold-quote
   and no-fold-literal.

      Message-ID-content = msg-id
      id-left            = dot-atom-text / no-fold-quote
      id-right           = dot-atom-text / no-fold-literal
      no-fold-quote      = DQUOTE *( strict-qtext / strict-quoted-pair )
                    DQUOTE
      no-fold-literal    = DQUOTE *( dtext / strict-quoted-pair ) DQUOTE

   A msg-id MUST NOT contain any SP within any strict-quoted-pair.  The
   msg-id MUST NOT be more than 250 octets in length.

        NOTE: The syntax ensures that a msg-id is restricted to pure
        US-ASCII, and is thus a strict subset of that defined by [RFC
        2822].  The exclusion of SP is to ensure compatibility with
        existing software.  The length restriction ensures that systems
        which accept message identifiers as a parameter when retrieving
        an article (e.g. [NNTP]) can rely on a bounded length. Observe
        that msg-id includes the '<' and '>'.

   Following the provisions of [RFC 2822], an agent generating an
   article's message identifier MUST ensure that it is unique and that
   it is NEVER reused (either in Netnews or email). Moreover, even
   though commonly derived from the domain name of the originating site
   (and domain names are case-insensitive), a message identifier MUST
   NOT be altered in any way during transport, or when copied (as into a
   References header), and thus a simple (case-sensitive) comparison of
   octets will always suffice to recognise that same message identifier
   wherever it subsequently reappears.

        NOTE: some old software may treat message identifiers that
        differ only in case within their id-right part as equivalent,
        and implementors of agents that generate message identifiers
        should be aware of this.

--- ../usefor-article-05/Message-ID.out          July 2001
+++ ../usefor-article-06/Message-ID.out          November 2001