This feature gives the option to regulate each role's message composing permissions.
Select the Messages tool from the Tool Menu in your site.
Permissions are assigned on a role-by-role basis. For instance, to prevent a student from sending a message to "All Participants," un-check the Student Permission box located next to the option, Allow send to 'All Participants' option.
Note: These options will be visible when clicking the "To" text box in Compose a Message, within the Message tool.
Click Save or Cancel to quit.