It was probably some teenagers with nothing better to do. Considering I used to be one of those as well and busted a few in my day. Unless you do something to protect your mailbox or setup some sort of surveillance system, thats really your only hope. It happens alot and alot of kids/people do it.

This is the only one that will take abuse from just about anything. Bats to bombs, its a tough cookie:



The concrete filled mailboxes aren't that great of a deterrent. Granted it hurts like hell one you hit, it generally only pisses the person off more and they'll keep coming back. The mailbox surronded in a brick column works great as well.