> Le 27 août 2023 à 16:32, Knute Snortum <ksnor...@gmail.com> a écrit : > > I think for the emails to thread, the subject lines must be the same (after > Re:).
This is not required. Each message contains an identifier (the Message-Id field, if you look at the raw email source), and if it's a reply, the identifier of the message it's replying to (the In-Reply-To header). All decent mail clients will will recognize these for the threading (though some clients like Evolution also have an option to fall back on subject-based threading, to cope with bad emails that lack the headers in question). The takeaway here is that "Reply" on an existing email and "New message" do different things even if the email subject, recipients and body are the same. If you want to reply in a thread, just use the "Reply" button in that thread.
