Thanks David for the script and the instruction. I am still not sure where notmuch is getting the association between my 5 messages in the thread. The attached pdf is the output of the script. As you can see the draft "draft-m25y9oqhep.fsf@gmail.com" which contains the header ,---- | From: Al Haji-Ali | To: bug-gnu-emacs@gnu.org, monnier@iro.umontreal.ca, Eli Zaretskii | Subject: bug#53632: Function definition history | In-Reply-To: | Message-ID: | Date: Sat, 22 Apr 2023 12:34:54 +0100 | X-Notmuch-Emacs-Draft: True | MIME-Version: 1.0 | Content-Type: text/plain `---- is completely unconnected the other 4 messages in the thread. Note that if I change the "In-Reply-To" field in this message to anything else, notmuch no longer groups these 5 messages into a single thread. I tried searching for "jwvczk7opm8.fsf-monnier+emacs@gnu.org" using `xapian-delve` but got ,---- | term 'jwvczk7opm8.fsf-monnier+emacs@gnu.org' not in database `---- Finally, I tried grepping for the same ID in my notmuch folder (with all mails and database) and got two hits (actually three including this message which I am currently writing): ,---- | ./Drafts/cur/1682165661.M337064P23717.m2air.local,U=151:2,DS:In-Reply-To: | Binary file ./.notmuch/xapian/postlist.glass matches `---- The first one is the draft. The second hit is the reason I thought the only place left for notmuch to associate these messages is in the xapian database. Note that if I delete the draft and reindex, only the postlist.glass hit stubbornly remains and there seems to be no way to make notmuch forget about this ID. I am running notmuch 0.37 and xapian 1.4.21 if that's relevant. -- Al