[Users] "Thread using subject in addition to standard headers" not working?

[Thomas Leitner]

On 2021-01-11 13:32 -0000 Paul wrote:
> On Mon, 11 Jan 2021 14:17:14 +0100
> Thomas Leitner <t_leitner at gmx.at> wrote:
>
> > This thread works because there *is* an In-Reply-To header as well
> > as a References header for all messages after the original one
> > (which obviously can't have such headers).
>
> Yes, so what's different about the your problem messages?
> In other words, you have not provided enough information about your
> query to be able to diagnose it.

I have written in the original message that those problem messages all
have *the same In-Reply-To and References headers*. And they don't
actually reference anything useful, i.e. sent or received mail messages,
but some meta information in the Jira ServiceDesk system.

My guess is that the occurrence of those headers with invalid data
throws off the threading and "thread using subject" algorithms.

-- Thomas