I recall reading on rec.crafts.metalworking, back in the day, of a couple guys that solved their mailbox issues, um.... creatively...
One used both sizes of official USPS tin mailbox, one inside the other, with reinforced concrete between the inner and outer ones. Said he found a broken baseball bat laying next to the mailbox, pretty much put an end to Mailbox Baseball, in his area...
The other guy, who had been having problems with keeping his mailbox due to a grader operator, carefully measured out the distance from the road centerline, augured a rather large hole, and concreted in a solid bar of six inch diameter steel to mount his mail box upon. The county Grader operator, who had been rather consistently taking out his mailbox, hit that, and sheared the mounts off the grader blade. Said THAT was what it took, to actually get the County Supervisor out on the scene. Didn't work so well for the Operator!