Glad your son was OK. Interesting about mailboxes, trees, rocks and insurance companies. A few years ago some drunk guy ran off the road in front of our house and plowed his car over our mail box into a small pile of boulders that sit amongst some pine trees about 10' off the road. He bounced between a couple of oak trees before he hit the pile of rocks. They stopped him. Understand, he was more than legally drunk, operating a motor vehicle, and damaged private property. Did I mention he was also a lawyer.
Anyway, he sued (filed a civil suit?) us for having the mail box, trees and rocks too close to the road, or something like that. Wanted $500,000 in damages, lost wages, pain & suffering, etc. We had to hire an attorney as our insurance company just laughed and denied his claim. The case was dismissed, and he had to pay our attorney fees. But what a pain in the rear. I had to miss work, file depositions, pay lawyer fees and then get reimbursed.
I've thought about changing our mailbox set-up to something less solid (my wife worries about someone actually hitting the post)....maybe the cantilevered type someone else here mentioned. Instead, for the time being anyway, I moved a couple of round boulders to protect the post. If they hit one of these at least they'll bounce off instead of hitting the railroad tie post directly.
There aren't any restrictions on mailbox post type, actual mailbox type, or even location where we live. The box has to comply with USPS regs, but that's pretty easy.
Anyway, rural mailboxes are always a topic for discussion out where we live.
Bob Pence