To the extent it's still relevant in the modern world, our postal system really needs to work a little more like the phone system.
I can be pretty much anywhere in the US (or really, the world, if I want to pay international roaming fees), someone can dial my well-known phone number, and my phone will ring.
For ordinary first class mail, I should be able to generate unique ID numbers on the USPS's website, and associate them with any physical US address I wish at any time. Then I can keep one or more postal IDs pointed at the location(s) I actually receive mail at, and the scanners (virtually all mail is routed by optical scanners now, even hand-addressed envelopes) can just read the ID number and stamp on the current physical address.