[no spam] ramifications_of_tweaks_to_subject_line :) - Was: ramifications of tweaks to subject line

RW rwmaillists at googlemail.com
Thu Jan 12 21:29:09 UTC 2017

On Thu, 12 Jan 2017 21:19:12 +0100
Ralf Mardorf via freebsd-questions wrote:

> Hi,
> I confirm Karl's reply regarding the headers.
> The thread is made of the email headers
>   Message-ID
>   In-Reply-To
>   References
> so as a reference actually
>   In-Reply-To
>   References
> could be used. The subject has nothing to do with the thread. Some
> MUAs allow to fall back to the subject, trying to workaround broken
> threads. A thread is broken, if there should be something fishy with
> the mentioned headers.

I don't know whether it's still the case, but there were some mail
systems that didn't preserve the original Message-Id, so In-Reply-To and
References could contain bogus values.  There's a rather complicated
document out there somewhere that details how to do robust threading
that takes account of this, and it does include the subject. Whether
any clients are still using this algorithm I don't know.

> My apologies for deforming the subject, but this might demonstrate
> that the subject is irrelevant, if the thread isn't broken.

It demonstrates that an exact match on subject is not the sole
mechanism, but we knew that anyway because that wouldn't allow for a
"Re: " prefix, or sub-threads. 

Note that your modified subject ended in the original subject, like an
ordinary reply would, just with a longer prefix.  

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