Question: My son is insisting that I can send him postcards to his name and 9-digit ZIP code, with no street address included. I don’t believe him. What’s the story and how do ZIP+4 ZIP codes work?

I need to know the rhyme and reason to zip codes. What prefixes are for what state? How and why they are structured the way they are. Also about the 4 digit extension to the zip code. How does that ...