Dave Crocker wrote:
the document asserts that more than one sometimes appear
in a message.
That is a bug. There should be precisely one Message-ID per
message, set by the UA or MSA / news / list server. When a
message without Message-ID hits a mail2news gateway, and the
gateway is not sure that there are no other gateways into
the same newsgroup(s), the broken message has to be dropped.
And a message with more than one Message-ID also has to be
dropped. In that case an error report to the broken MSA
could help, IIRC MSAs are supposed to enforce 2822 syntax.