Message My Teacher Block
Message My Teacher is a very simple block. It will display a list users who are teachers for the current course with links to send them a message.
The block requires that you select the roles you wish to consider "teachers" (those who will appear in the block). In Site Administration/Plugins/Blocks/Message My Teacher you can select as many roles as necessary by checking the appropriate boxes.
Anyone visiting a page with the block on will see a list of all users with the selected roles. Clicking the user's name will take them to a screen allowing them to compose a message to that user. Note: users will never see their own name on this list, as they will never need to message themselves. If they are assigned the appropriate role, they will still appear to other users.