>The additional complication was that the USPS wouldn't deliver to the house, so they got a PO box, which is common in rural areas. But the USPS won't allow private carriers to deliver to PO boxes. So you need to use a different address depending on which carrier is taking the package. A lot of stores (Amazon!) won't tell you which carrier they're going to use!

Two options:

* Specify both the PO box and street address in the mailing address, like

John Q. Public

PO Box 123

1 Main Street

Anytown USA 00600

This is best for situations where you don't know which carrier the sender will use. People who live in rural areas where they have both a PO box (because USPS won't deliver to their homes) and a valid street address that other carriers do deliver to might use this option.

* USPS PO boxes can receive from other carriers, if street addressing is used. <https://www.usps.com/manage/po-boxes.htm#streetaddress>