Re: 202212160543.AYC Re: eMail Conventions

[Joel Esler via NANOG <nanog () nanog org>]

> 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 <mailto: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).

…. and now that I wrote the above email response, I think you’re right.  In-Reply-To:  I believe, is how Mail.app does 
it. (And several others)