How forums only to send messages to teachers. Thank !
You can create a forum for teacher discussions if you hide it for students. If you want that only teacher can see the posting you can use the messenger or the online assignment type.
I think the question is how to have all forums only email teachers. If so a solution that occurs to me is Administration ► Users ► Permissions ► Define roles student Set Initial and Manage subscriptions to no then set the student profile to not subscribe to forums when they post.