We have zero plans for topic based user permissions for the forseeable future, so I suggest you use different software if that is a hard showstopper requirement.
Your options are
- email into
help@example.comwhich automatically creates a PM to the@helpgroup in Discourse, and already works today. We use it this way in fact..
or
- User starts PM like any other PM
- User selects
@helpgroup as the target for the PM. - Topic is visible to author only, and the
@helpgroup