[Harald Meland]
(Not having read c.l.p,) I don't understand how such a proposition could generate much of a discussion :)
Having read the discussion in c.l.p, I now understand :)
If an email contains an In-Reply-To: header, I'd guess it is due to it being a reply. If this email is gated to news, the fact that it is a reply, and preferably what message it is a reply to, should be indicated somehow.
If such an indication can only be given by having the news-gate muck around with the headers of the message, _and_ such mucking won't destroy any of the _original_ headers of the message, I don't really see the harm.
... and before anyone gets religious on me here, I'll rush to explain that I _do_ see the harm of inserting "faulty" References: headers -- any In-Reply-To: candidate should at the very least be in the form of a valid message ID.
I think there was a slightly similar discussion on the (ding) Gnus mailing list a while back -- it was spurred by the fact that Gnus' threading sometimes broke down, as some mailers put several message-id-look-a-like-tags (e.g. mail addresses in angle brackets) in their In-Reply-To: header.
Thus, Mailman should be very conservative when moving MessageID-candidates from In-Reply-To: to References: -- it might even be a good idea to query the newsserver whether it has the candidate replied-to article (even though that probably won't work with all newsserver configurations).
If the appropriate level of conservatism can be reached without making the involved code *too* complex, I still believe this particular case of header mucking could be a Good Thing.
Harald