Bruce Lilly writes:
[ ignoring newer USENET docs, and apparently misrepresenting RFC 2822 ]
While RFCs 1036 and 2822 suggest ordering of the msg-ids in the References
field, there is no requirement to use a specific ordering. In particular,
UAs should not presume that the order of appearance of msg-ids in a
References field is significant.
In the real world, UAs do pay attention to the order inside References.
It's particularly important for References to start with the thread ID
and end with the parent ID.
My understanding is that trn---which uses References to construct a
thread picture even when some messages are missing---works best when
References is sorted. This is violated by some of the multiple-parent
proposals. Perhaps multiple parents should be handled by simply
* creating a References field from the newest parent and
* creating an In-Reply-To field from all the parents.
But I wouldn't support this proposal, or any other proposal, without
seeing a careful investigation of current thread-displaying software.
---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago