To prevent users from sending messages to the admin user, use the setting at {your.forum}/u/admin/preferences/users, which merefield mentioned. Staff can always send messages to users, so test with a regular user account.
To prevent users from sending messages to the admin user, use the setting at {your.forum}/u/admin/preferences/users, which merefield mentioned. Staff can always send messages to users, so test with a regular user account.