Note: the real barcodes use 11 digits. There are two extra digits beyond the Zip+4 that encode the stop along the route. The Zip+4 gets you to the block but then you need two more digits to specify the house/apartment etc. If you can decide the barcodes sprayed on the front of the envelope by the USPS, you'll find the extra two digits. But the Zip+4 that everyone knows isn't that precise.
