What are the requirements for a roadside mailbox?
The United States Postal Service (USPS) provides standards for mailboxes on the side of the highway. The mailbox should be 41-45 inches above the road surface and 6-8 inches from the face of the curb or road edge. This is done to allow the postal carrier to drop off the mail without leaving the vehicle. If done properly, this allows a snow plow to clear the road without destroying the mailbox. The mailbox should not be put in such that it becomes a fixed object and the box should be properly attached to post so that it does not fly away when struck. The two videos show examples of a rigid mailbox and gang mailbox that are unsafe and should not be used.
Dangerously designed rigid mailbox
Dangerously designed gang mailbox
This video shows a mailbox that is crashworthy.