According to Amazon:
https://www.amazon.com/gp/help/customer/display.html?nodeId=201117330
Address Format.
If a post office box address was entered in a format our system
does not recognize, the package may be shipped through a carrier that
cannot deliver to a post office box. To ensure that such packages are
routed through the proper carriers, please enter the box number as "PO
BOX" followed by the number. Also, if you're a private mailbox holder
(use a local commercial mail receiving agency), do not use "Box" for
your mailbox number, instead use # or PMB. This will ensure that your
address is not mistaken to be a P.O. Box, and that orders can ship to
you via means other than the U.S. Postal Service.
Of course I'm assuming you're talking about a PO box or a mail drop.
And that you're talking in the US.