Place your mailbox at the street end of your driveway or next to your front door. For street boxes, you will need to anchor a sturdy support post in the ground no more than 24" deep. The post should be tall enough for the bottom of the mailbox to sit between 41" and 45" in height above the street surface. Place the post 6" to 8" back from the curb or street. A wall mounted mailbox must by 30" above the floor level at the exterior of the house. The slot must be 1 1/2" high by 7" wide. Horizontal slots must be hinged and vertical slots must be placed opposite the front door hinges.