I have a use case where a course lecturer sends the same questionnaire via PM to the course participants occasionally, but wishes to receive separate responses from each one.
Being able to assign a custom group (e.g. organizers) in addition to staff to use the BCC plugin would solve the problem for them in a big way (they’re currently sending dozens of identical PMs).
@md-misko - I wonder if your need might be met by the Discourse Private Replies plugin. Basically, you’d create a course category with access for the participant group, rather than using PMs. The plugin can then keep replies to a lecturer topic hidden from other participants.
(A caveat is that any subsequent reply from the lecturer back to a participant is visible to all. Depending on your situation that may or may not matter.)