Dien, when you have a chance, do some testing on the Private Messages feature...
I've been using it to email some registered users but after I hit the forum send button it's not showing as sent or recording any inbox or sent details.
The email seems to get sent and received ok after confirming things But doesn't show in the forum Private Messages feature.
I know you can send messages using your own email or through the forum system so maybe it just requires some setup by you or maybe each member, although it's always worked automatically on other vBulletin forums. No emergency, just thought I'd let you know.
Thanks again for all your hard work.