StopForumSpam explained?

[infinitys]

Options in approval queue:

Do nothing- does that just leave them in queue forever?
Spam clean?

Approval and reject are self explained. Is there a way to send them to a usergroup where they can only dm staff if legit and turn off permissions to post and receive emails?

 

[Kirby]

Do nothing- does that just leave them in queue forever?

Yes.

Spam clean?

Invokes the spam cleaner as configured by admin.php?options/groups/spam/

Is there a way to send them to a usergroup where they can only dm staff if legit and turn off permissions to post and receive emails?

Yes, but the highlighted part is not possible with stock XenForo - this would require custom development.