usefor-article-13 May 2004

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]
   (but see the revised definition of msg-id in section 2.4.3).

      header             =/ Message-ID-header
      Message-ID-header  = "Message-ID" ":" SP Message-ID-content
      Message-ID-content = [FWS] msg-id [FWS]

   The msg-id MUST NOT be more than 250 octets in length.

        NOTE: 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 '>'.

        Observe that, in contrast to the corresponding header in [RFC
        2822], the syntax does not allow comments within the Message-
        ID-header; this is to simplify processing by relaying and
        serving agents and to ensure interoperability with existing
        implementations.

   An agent generating an article's message identifier MUST ensure that
   it is unique (as also required in [RFC 2822]) and that it is chosen
   in such a way that it will NEVER be applied to any other Netnews
   article or Email message. However, an article emailed (without
   encapsulation) to a moderator (8.2.2 and 8.7) or gatewayed into some
   other medium (8.8.1) SHOULD retain the same message identifier
   throughout its travels so long as it remains recognizably the same
   article.

   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 recognize that same
   message identifier wherever it subsequently reappears.

        NOTE: These requirements are to be contrasted with those of the
        un-normalized msg-ids defined by [RFC 2822], which may perfectly
        legitimately become normalized (or vice versa) during transport
        or copying in email systems.

        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-12/Message-ID.out          November 2003
+++ ../usefor-article-13/Message-ID.out          May 2004