In Moodle 3.6 message contacts are reciprocal relations and require approval from the other users, see MDL-63211. This feature is being developed for web and there is no UI design yet.

Needed changes:

• Display list of pending contact requests.
• Approve / decline contacts requests.
• Handle notifications of contact requests.
• Use new web services for handling contacts.
• Don't allow sending messages to non-contacts depending on user preferences.