usefor-article-04 April 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 [MESSFOR],
   subject to the following revised definition of no-fold-quote.

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

   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 in strict compliance with [MESSFOR]).  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 '>'.
[Do something about whitespace in dot-atom-text and no-fold-quote.]

   Following the provisions of [MESSFOR], 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-03/Message-ID.out          February 2000
+++ ../usefor-article-04/Message-ID.out          April 2001
@@ -4,22 +4,31 @@
    unique identifier distinguishing the article from every other
    article. The content syntax makes use of syntax defined in [MESSFOR],
    subject to the following revised definition of no-fold-quote.
+
       Message-ID-content = msg-id
       id-left            = dot-atom-text / no-fold-quote
       no-fold-quote      = DQUOTE *( strict-qtext / strict-quoted-pair )
+                    DQUOTE
+
+   The msg-id MUST NOT be more than 250 octets in length.
 
- NOTE: This syntax ensures that a msg-id is restricted to pure
- US-ASCII (and is thus in strict compliance with [MESSFOR]).
+        NOTE: The syntax ensures that a msg-id is restricted to pure
+        US-ASCII (and is thus in strict compliance with [MESSFOR]).  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 '>'.
+[Do something about whitespace in dot-atom-text and no-fold-quote.]
 
    Following the provisions of [MESSFOR], an agent generating an
    article's message identifier MUST ensure that it is unique and that
-   it is NEVER reused. 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.
+   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,