What could pull down a brick mailbox?

As a former rural mail carrier I have seen this problem often. Most of these mail boxes have very shallow foundations. A truck backing into this type of mailbox can easily knock one over. A car could hit it and knock it over, although there would be a lot of damage to the car. These type of mailboxes can be very dangerous if a car is going at a highway speed and then looses control and hits one. They should never be used where traffic is not usually very slow.