The whole postal system lacks the equivalent of a DNS layer. You don't manually type in 66.249.85.99, you go to www.google.com. Likewise, you shouldn't have to jot down the complete, current physical address of anyone. Instead, people and companies should have unique "mail names"; you would simply put down the mail name of the person you want to send something to, and the postal service would look up their current address and send it to them.

All it takes is some rudimentary insight on behalf of the Postal Service to put this into action, and it would greatly improve the reliability of mail for everyone.