looking for Cyrus mail format documentation

[Jason Fesler]

> However, had message IDs been the RFC822 message ID, then it would have
> been possible to receive new mail on each node.  Since the IDs would not
> collide, that would be OK.  If you did get the same ID delivered to both
> somehow, it should be the same mail.  If not, it violates the RFC, so
> then you decide to replace one of them or change one of them and move on.

Perhaps the same mail, but with different Received: headers, and possibly
with mailing list software headers added.  IMO, "Message-Id:"  is not
strong enough of a UIDL, *especially* for list owners.