Quote Originally Posted by Avlvs Libvrnivs Britannicvs Maximvs
He means they get deleted when your PM box reaches it's limit. This means that, if your box is full, then your oldest PM gets deleted the moment you get a new one in that would cause you to exceed the limit.
I don't think it does. If you try and pm someone when their inbox is full you get a message saying "pm can't be sent".