Yes, there are govt. regulations on mailboxes. Years ago, I got tired of people running over my mailbox. So, I built one out of 8" pipe, and set it 3' in the ground in concrete on a 3" post. Had to set it with a front end loader. It got hit once, but it totaled the front end of a pickup. LOL. The post office inspector came out and told me it was illegal. Now, I have a P.O. box. I still get mail at the gate, but it is recessed from the road. Charlie
The PO regulates and approves the mailbox. The DOT, fed hwy admin and county, state and local governments dictate placement on their right of way.
Place a 3' x 3' brick column with a mailbox in it and the carrier will deliver your mail. Let a teen driver run off the road and hit the road hazard you placed on the right of way and look out for the lawyers knocking on your door.
Minnesota passed a law in 1991 that gives them the right to take your box down and charge you for the work.
There was a bit of public outcry locally when notices started showing up in mailboxes that their box was non-compliant, and they would have to start picking their mail up at the Post Office until it was corrected.
Residents complained, and were given specifications for mailbox placement.
One such box was only 1 inch higher than specs, and that was because the mail carrier's car had rutted out the area in front of the post.
It seems there was a new lady carrier on this route, and it was forcing her to make some effort to deliver the mail.
I believe they have settled on some neutral ground.