Dave,I don't expect nor are any our mail software designs, main mail processors, distribution, dupe checkers, tracers, gateways or all other mail utilities support a silly concept of multiple Message-id: headers per message. Of course, it may exist but only one is truly valid. I personally never seen or don't recall ever seeing multiple message-id: lines and I can't imagine at this time what would be the effect other than only the first or maybe the last one is used.
It is possible there was a mis-communication with your challenger in regards to the References: header which includes a list of multiple messages ids?
Dave Crocker wrote:
Folks,The email-arch specification notes that Internet standards provide for at most one Message-ID, but the document asserts that more than one sometimes appear in a message. I put that in because that's been my impression.THe assertion has been challenged. Easiest way to resolve this is to query the community.So, Community, I'm querrying you: Do you see multiple message-id's in messages? If you do, what affect do they have? d/
-- HLS