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

[Paul]

On Mon, 11 Jan 2021 09:26:01 +0100
Thomas Leitner <t_leitner at gmx.at> wrote: 

> Yes, all the messages are in the same folder. However, how would Claws
> determine the "parent message" if threaded by subject? Because the
> In-Reply-To and References headers of all those messages are the same
> in my case.

Look at this thread, which your original message started. Your original
message (the parent) obviously doesn't have a References header or an
In-Reply-To header.

with regards

Paul