On Thu, Aug 27, 2026 at 14:38 +0200, Arnt Gulbrandsen wrote:
JFYI, this was discussed in the IETF working group during the work on
either 2822 or 5322, I think it may have been in 2003 or 2004 but don't
hold me to that.
A mail thread is not necessarily a tree. Many people want it to be,
much software expects it to be, but that relies on cooperation by
everyone, and some email software doesn't cooperate.
Well, sure. Email is very old, is implemented almost everywhere, and
has changed a lot; it's inevitably imperfect. Mutt itself allows the
user to generate a reply to multiple messages. I think that's OK; I
just think it should not generate References: for multiple parents.
The conclusion at the time was twofold. ① In-Reply-To should name all
the messages to which this message is a direct reply. ② References
should contain the References of the message being replied to and
Message-Id of that message, if this message is a reply to a single
message. ③ There is no specified algorithm for constructing References
for a message that is a reply to several messages. I think someone
mentioned a MUA that can construct such replies, one with a four-letter
abbreviation as name, but nobody wanted to discuss this in detail or
standardise it. Yes, this is the third point in a two-point list, and
it's a no-op.
That's what I got from reading RFC 5322.
