How to enable private messages notifications for vBulletin users?
You can allow all vBulletin forum members to receive private messages by running a query under the vBulletin admin area -> Maintenance -> Execute SQL Query. Pick the Yes - Receive Private Messages option from the Automatic Query drop-down menu. Then run the query by clicking on the Continue button.
If you want to enable the notification e-mails when private messages are received navigate to the same area (vBulletin admin area -> Maintenance -> Execute SQL Query) and pick the Yes - Send Notification Email When a Private Message is Received option. Again, click on the Continue button to execute it.
The third option associated with the private messages is related to the notification box that can pop-up when a private message is received. To enable it pick the Yes - Pop up a Notification Box When a Private Message is Received option.