Like Marlys - we have no home mail delivery in our town. But I live out in the county so we have to either have a mail box or rent one from PO. As others have said - you can go on line and find out where someone lives - I just googled my dtr who has an unlisted phone and got her address and approximate age. Some companies I buy from only ship via USPS so I give them my company's PO box number just so I can pick it up when I go daily to pick up our mail. That way they don't have to leave me a note that says come to the PO. I just received a package yesterday that our mail carrier actually put on my front porch & left me a note telling me it was there. Our postal employees really go out of their way to help.
The only important mail I get is two utility bills and one for trash pick up. All other bills/checks are direct deposit/withdrawal.