Moodle messaging is a fantastic tool but it is often abused by our students here at college. Students have been reported to spend too much time sending messages in class. Often the male students spend time looking for female students to whom they can send a message to.
When a student receives an unwanted message they can report it by clicking a link.
This then gets emailed to me and I can remove messaging rights for the offending user.
To do this I created an extra field in the mdl_user table called message_ban. I then added some code to the message pages in Moodle which checks againt the user ID and the message_ban field. If the user is banned they can no longer use the messaging system and they are greeted with the following message.