Tomi Ollila <tomi.ollila@iki.fi> writes:

> (One thing to remember (for anyone perhaps planning to do something about
> this) is that if we'd use Resent-Message-ID: as message identification 
> if it exists, then Message-ID: of the message should act as In-Reply-To:
> or References: -header...)

It actually seems like one of the more benign cases of message-id
collision that currently exist in notmuch. The fact that by default you
see only one copy of a message that arrived two different ways is a
design choice; it's hard to get closer than the resent message case.  I
suspect any change would have to be configurable, since most existing
notmuch users would be pretty surprised to suddenly see lots of
duplicate messages.

d