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Problems with in-reply-to threading

2001-08-31 05:03:52

recently I have had some problems with messages being threaded inappropriately in my (IMAP) inbox.

Being the kind of person I am, I more or less hunted it down, finding these gems:

1) Header:
In-Reply-To: Message from Harald Tveit Alvestrand 
of "Fri, 06 Jul 2001 13:17:51 +0200." <759246899(_dot_)994425471(_at_)[192(_dot_)168(_dot_)1(_dot_)31]>

2) RFC 2822:

4.5.4. Obsolete identification fields

  The obsolete "In-Reply-To:" and "References:" fields differ from the
  current syntax in that they allow phrase (words or quoted strings) to
  appear.  The obsolete forms of the left and right sides of msg-id
  allow interspersed CFWS, making them syntactically identical to
  local-part and domain respectively.

obs-message-id  =       "Message-ID" *WSP ":" msg-id CRLF

obs-in-reply-to =       "In-Reply-To" *WSP ":" *(phrase / msg-id) CRLF

Note the absence, inherited from 822, of anything indicating the proper
content of a "phrase".

3) THREAD specification - draft-ietf-imapext-thread-07, section 6.3:

           If a message does not contain a References header line, or
           the References header line does not contain any valid
           Message IDs, then use the FIRST (if any) valid Message ID
           found in the In-Reply-To header line as the only reference
           (parent) for this message.

              Note: Although RFC 822 permits multiple Message IDs in
              the In-Reply-To header, in actual practice this
              discipline has not been followed.  For example,
              In-Reply-To headers have been observed with email
              addresses after the Message ID, and there are no good
              heuristics for software to determine the difference.
              This is not a problem with the References header however.

           If a message does not contain an In-Reply-To header line, or
           the In-Reply-To header line does not contain a valid Message
           ID, then the message does not have any references (NIL).

My capitalization.

Even more worrisome is this header:

References: <harald(_at_)alvestrand(_dot_)no>

which was apparently created on the basis of a different incarnation of the previous one, following the algorithm of RFC 2822 section 3.6.4:

  The "References:" field will contain the contents of the parent's
  "References:" field (if any) followed by the contents of the parent's
  "Message-ID:" field (if any).  If the parent message does not contain
  a "References:" field but does have an "In-Reply-To:" field
  containing a single message identifier, then the "References:" field
  will contain the contents of the parent's "In-Reply-To:" field
  followed by the contents of the parent's "Message-ID:" field (if
  any).  If the parent has none of the "References:", "In-Reply-To:",
  or "Message-ID:" fields, then the new message will have no
  "References:" field.

(It seems to have missed the part about In-Reply-To field containing a single messgae identifier, though...)

The product creating the initial problem seems to be an MH variant's group-reply-to init file (replgroupcomps); we can fix it one install at a time, but this seems like a glorious time for clarifications....

Suggested fixes:

1) In RFC 2822bis, state that the msg-id form of obs-in-reply-to MUST contain a message-ID, and NOT an email address (a "phrase" cannot contain an unquoted angle bracket, so it is only the msg-id that allows it)

2) In RFC 2822bis section 3.6.4, state that the In-reply-to should only be used to form References if it has a single message-ID, and that the reason is that users of obs-in-reply-to sometimes put emails in their in-reply-to fields.

3) Unless someone says that a reasonably widespread implementation exists that puts FIRST a message-ID and THEN an email address into the in-reply-to field, change the THREAD specification to pick up the LAST instead of the first identifier.

What do people think?


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