Mark Walters <email@example.com> writes: > > I have looked at this and I think this is not notmuch's fault: I think > it is a mua doing strange things: > > One of the mails has an in-reply-to header which looks like > > In-reply-to: Message from Carsten Dominik <firstname.lastname@example.org> of "Tue, 15 Mar 2011 12:18:51 BST." <17242340-A14F-495A-B144-20C96D52B620@gmail.com> > > and I think notmuch is taking the email@example.com as message > id. > > A similar in-reply-to header appears in the other thread so notmuch > pairs them up. According to http://www.jwz.org/doc/threading.html this > form of header is not allowed under RFC2822 but was allowed under the > earlier RFC822. I have identified a second, similar problem. Some MUA insert(s|ed) the From: address into the References field. For an example see id:firstname.lastname@example.org https://email@example.com/msg24266.html This seems to be another throwback to rfc822 I don't know how notmuch can detect this once it those references propagate to replies. - we could merge threads only based on messages known to exist (ignoring ghost messages), but presumably there's a reason we invented ghost messages - we could, at some point in future support blacklisting references (using message properties).