Disabling a school will stop all admin, teachers, and non-rostered staff from sending messages.
Navigate to the 'Schools' tab in the sidebar, and select the school you would like to disable from the list. Click on 'Disable School'.
To let school admins and teachers send messages again, navigate to the 'Schools' tab in the sidebar, and select the school you would like to enable from the list. Click on ‘Enable School'.