Managing personal message participants

[JammyDodger]

I’m afraid this is currently not possible, but there is an open #feature request discussing the issue here:

Prevent adding additional users to personal messages?

Hi there. I’m seeing concerns from users about the ability to add additional users to a personal message topic who can then see the entire message thread, resulting in a possible intentional or unintentional doxing if somebody posted private information earlier in the thread. The expected behavior for these users is that added users would only be able to view the personal message topic from the point where they were added. This sounds ideal to me too, but hard to implement from the Discourse po…