History of ZIP+4
Where the nine digits came from, and what each one does.
Updated August 2026
Guides
Everything we know about US addressing, written out properly. No fluff, no affiliate padding, and every USPS fee dated so you can tell when it went stale.
Moving & address change
File the USPS change, then work the list of everyone else.
Updated August 2026
Mail forwarding
What gets forwarded, for how long, and what silently does not.
Updated August 2026
Address labels
Get the address right before you print five hundred of them.
Updated August 2026