Friends in Ontario, CA say that a lot of their mail is misdirected to CANADA, very often they get it too late to attend events, etc.
So be sure to write out the address totally, with the ZIP in large letters, then put 2 inch wide clear tape over it. Then ask the postal clerk to put tape on the computer generated label. And be sure to put both your and the addressees names and addresses on a big piece of paper inside the package.
That way there's no way they can get it the wrong way.
Oh..we're talking about the USPS? Well................