Delivery costs have plummeted because of the enormous amount of machine intelligence being used by courier companies. Better routing algorithms reduce fuel and staffing costs, better machine vision technology allows package labels to be read and sorted at high speed. Mail-order companies and delivery services have formed a symbiotic virtuous circle of business development - greater volumes of mail reduce per-unit costs, which encourages an increase in volume. Amazon are the prime (no pun intended) example of this, with their progressive diversification into selling bulkier and lower-value items.