Hi there, > On 16 Dec 2022, at 17:13, William Herrin <b...@herrin.us> wrote: > > Most email clients assume that a change to the subject line (other > than adding "Re:" to the front) indicates that the sender wants to > discuss a new topic related to but meaningly different from the last.
Although I generally agree that changing the Subject line without reason is an annoyance, I didn’t notice any issue with it until I came across this thread, which wasn’t broken in my mail client (Apple’s Mail.app). This led me to a few tests, and FWIW even Mutt seems happy with the Subject changing and still threads the emails appropriately. In my experience, threading is done by clients looking for the In-Reply-To: header, not subject. Subject is a heuristic fallback, in case In-Reply-To is absent. Some email clients (although I don’t remember which ones) remove In-Reply-To: when the Subject: is changed (that might go as far back as my Gnus Oort days). BR, ic.
