I’ve not found this request, but my apologize If I’ve missed it.
When we manage an issue by mail, we have encountered at least two case where delete a specific message on the thread could be useful.
First case is bot reply, in some case some contact have an antispam or a any automatic reply. Could be interesting to delete it to get an intelligible thread.
Second case, is an error when we add/move a contact with a different mail. An error on the mail and we can get a bounce error or any message. In this case we correct message but previous bad is again present.
Purpose is not delete thread issue, but in some case target specific message on the issue and delete them to conserve a intelligible issue.
Could be possible ?