usefor-article-08 August 2002

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 definitions of msg-id, no-
   fold-quote and no-fold-literal.

      header             =/ Message-ID-header
      Message-ID-header  = "Message-ID" ":" SP Message-ID-content
                    *( ";" other-parameter )
      Message-ID-content = [FWS] msg-id [FWS]
      msg-id             = "<" id-left "@" id-right ">"
      id-left            = dot-atom-text / no-fold-quote
      id-right           = dot-atom-text / no-fold-literal
      no-fold-quote      = DQUOTE
                    *( strict-qtext / "\\" / "\" DQUOTE )
                    qspecial
                    *( strict-qtext / "\\" / "\" DQUOTE )
                    DQUOTE
      qspecial           = "(" / ")" /        ; same as specials except
                 "<" / ">" /        ; "\" and DQUOTE quoted
                 "[" / "]" /
                 ":" / ";" /
                 "@" / "\\" /
                 "," / "." /
                 "\" DQUOTE
      no-fold-literal    = "[" *( dtext / "\[" / "\]" / "\\" ) "]"

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

        NOTE: 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.

        The restriction to strict-qtext ensures that no UTF8-xtra-char
        can appear. Msg-ids as defined here are a "normalized" subset of
        those defined by [RFC 2822], ensuring that no string of
        characters is quoted unless strictly necessary (it must contain
        at least one qspecial) and no single character is prefixed by a
        "\" in the form of a quoted-pair unless strictly necessary, and
        moreover there is no possibility for WSP to occur, whether
        quoted or not. 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 '>'.

   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 recur in either 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 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-07/Message-ID.out          May 2002
+++ ../usefor-article-08/Message-ID.out          August 2002
@@ -3,13 +3,14 @@
    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.
+   2822], subject to the following revised definitions of msg-id, no-
+   fold-quote and no-fold-literal.
 
       header             =/ Message-ID-header
       Message-ID-header  = "Message-ID" ":" SP Message-ID-content
                     *( ";" other-parameter )
-      Message-ID-content = msg-id
+      Message-ID-content = [FWS] msg-id [FWS]
+      msg-id             = "<" id-left "@" id-right ">"
       id-left            = dot-atom-text / no-fold-quote
       id-right           = dot-atom-text / no-fold-literal
       no-fold-quote      = DQUOTE
@@ -28,27 +29,34 @@
 
    The msg-id MUST NOT be more than 250 octets in length.
 
-        NOTE: The restriction to strict-qtext ensures that no UTF8-
-        xtra-char can appear. Msg-ids as defined here are a "normalized"
-        subset of those defined by [RFC 2822], ensuring that no string
-        of characters is quoted unless strictly necessary (it must
-        contain at least one qspecial) and no single character is
-        prefixed by a "\" in the form of a quoted-pair unless strictly
-        necessary, and moreover there is no possibility for WSP to
-        occur, whether quoted or not. 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 '>'.
+        NOTE: 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.
+
+        The restriction to strict-qtext ensures that no UTF8-xtra-char
+        can appear. Msg-ids as defined here are a "normalized" subset of
+        those defined by [RFC 2822], ensuring that no string of
+        characters is quoted unless strictly necessary (it must contain
+        at least one qspecial) and no single character is prefixed by a
+        "\" in the form of a quoted-pair unless strictly necessary, and
+        moreover there is no possibility for WSP to occur, whether
+        quoted or not. 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 '>'.
 
    An agent generating an article's message identifier MUST ensure that
-   it is unique (as also required in [RFC 2822]) 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 recognize that same message identifier wherever it
-   subsequently reappears.
+   it is unique (as also required in [RFC 2822]) and that it is chosen
+   in such a way that it will NEVER recur in either 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 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