the US postal service works fine, just like our own.......
When away for a while in the US the collection of stuff builds up, a visit to the post office to send back my regular Aussie clothing I took with me works just fine enabling me to take all my new goodies with me on the plane. I find US post workers most helpful, even searching the back of the office to fine me a box to put things in and at no charge.
Works better at smaller post offices, but smarter to find you own box than hope they can find one for you.
I even sent back a box of gilsonite once which made it fine (a coal like mineral trench mined in the back blocks of Utah), the only problem was washing it in the motel bath tub left the tub stained black, but that's another story.