On our site, users with the ‘student’ role are not allowed to write messages in the private messaging system. To implement this prohibition, we removed all permissions for the roles ‘student’ and ‘authenticated user’ regarding ‘message’:

Technically, we got the expected result: users without the role ‘teacher’ or ‘administrator’ cannot initiate a dialogue or send a message in a dialogue started by another user. This is exactly what we need - teachers and administrators can correspond and make newsletters, but students cannot.
However, the button to send messages from the student interface has not disappeared, and if he tries to reply to someone who has written to him, an error ‘error/User N cannot send a message to conversation M’ occurs when he presses it. 

Are there no prettier ways to achieve what we need?