ZIP Code How is the Zip plus Four determined.?

Question

Why does it seem as though everyone knows my entire zip except me. I have never been notified what it is or how it is determined.

Answer 1

actually you are notified by the USPS.
when u move or change your address at the post office they sent u the first mail with your new and old addresses including your zip.
zips are usually divided by cities, counties, blocks/buildings (if u live in downtown of a big city) etc.
hope this helps.