Your local post office probably. I assume the builder has to file a new address with them.
am i screwed if i already forwarded my mail? it doesn't seem to exsist. i checked on www.smartystreets.com they had nothing.
How could USPS let you forward mail to a non existent address?
Do you have a CO?
Go to USPS.com and put in your address. See if it comes up with a zip+4.
How would you know?!
Read it on some blog.