Part 1- Officezip BEST
The ZIP+4 code is not required, but it aids the post office in additional sorting of mail. A ZIP+4 code may correspond to a city block, group of apartments, oran individual high-volume receiver. It is also common for each PO Box number to correspond to a unique ZIP+4 code. Sometimes, several PO Box numbers are grouped intothe same ZIP+4 code by using the last several digits of the PO Box number. This method isn't a universal rule though so the ZIP+4 must still be looked up for each POBox.
Part 1- officezip
Remember that ZIP codes were made to make mail delivery easier. They weren't made to correspond to existing boundaries suchas cities, counties, or even states. If it is more efficient for a mail carrier to drive across a state line to deliver mail, the ZIP code"boundary" will cross the state lines. ZIP codes don't usually cross state lines, but some do (65733, 71749, and 73949 are good examples).The complete list of ZIP codes that cross state lines is available as part of our US ZIP code list. 041b061a72