On Thursday, 22 September 2022 at 16:30:05 UTC+1, Max Nikulin wrote:
...
Debian mail list archive has a rare mhonarc configuration that adds
reply to list action (usually only reply to sender is available) and
these mailto: links contain proper In-Reply-To value
https://lists.debian.org/debian-user/2022/09/msg00584.html
Even groups.google.com is unable to render proper discussion tree, its
representation is a list.
Mail user agents may intentionally suppress threads based on heuristics
to avoid combining unrelated discussions having subjects like "question"
or "problem".
thanking all for the observations + information. I have had a look in
settings of Gmail, my "mua", and cannot find an obvious (any!) place
where headers could be set (and haven't the knowledge, anyhow). so, I
won't try and start any more threads for now (for which sorry) and
hope that someone can/will supply Gmail specific instructions "how
to"; to that end please write an email with 'mail headers' in the
subject, thank you.