Comment by chickenWing

Not only that, but don't rely on third-party services to do your validation for you, and yes, that includes the US Post Office, if you're looking for a physical address. There are many physical addresses in the United States that the Post Office doesn't deliver mail to, and yet people live there. I know because I live in one of those places. UPS and Fed-Ex have no problem finding the address, but for regular mail I have to use a PO Box. It is frustrating when I don't know which method an online store will use. It is also frustrating when a site repeatedly tells me my address doesn't exist.