On Dec 16, 2022, at 12:04 PM, ic <lists@benappy.com> wrote:

Hi there,

On 16 Dec 2022, at 17:13, William Herrin <bill@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).

As a user of Mail.app as well, it is not broken for me either. However, reason being — Mail does not use just the subject to thread. I used to nerd out about email (top + bottom posting, etc) so the details of how Apple Mail threads have been lost in my ADHD riddled brain, but — that’s why.

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).