If you have a p.o. box and have a problem with a company needing a street address the post office lets you sign up for “street addressing” for your p.o. box at no cost. So when someone ships something UPS or FedEx or just needs a physical address you give them the street address of the post office, and the box number as the “secondary address” line. Such as 123 Main St. #4567. If this was your post offices address and you had p.o. box 4567. And if something comes UPS or FedEx they deliver to the back door of the post office and then the post office delivers it (or leaves a notice) in your p.o. box. I am a clerk for the post office and if I get an RV this is what I’m going to do.