> On Sep 25, 2023, at 06:52, Teemu Likonen <tlikonen@iki.fi> wrote:
> 
>> Some person on debian-user mailing list seems to be sending messages
>> with fixed Message-ID field: the same ID in different messages. In
>> Notmuch it is creating trouble because it connects unrelated threads to
>> one. The person has different messages in different threads but Notmuch
>> thinks they are the same message because the Message-ID is the same.
>> 
>> This is potentially a "denial of service" for Notmuch. Well, not quite,
>> but is harmful nonetheless. How would a Notmuch user fix the mess or
>> protect himself against it?
> 
> I am no longer sure if this issue is caused by fixed "Message-ID" or
> wrong "References" or "In-Reply-To" values. Anyway, someone has created
> real mess anyway because Notmuch combines originally separate threads
> now and forever.

Silly question, I know, but have you actually tried reaching out to the user?  No MUA that I’m aware of acts like this and it’s pretty clear from documentation and standards tracks that Message-ID is meant to be globally unique per message.

If the user is knowledgeable enough to have a boutique mail reader, they’re probably also knowledgeable enough to correct the defect too.