I thought this was "fake news" when I read about it, but it seems to be true, and is really really handy for those of us who live in the middle of nowhere and rely on Amazon Prime and other by-mail suppliers:
http://givebackbox.com/
Way it works is simple: You receive your shipment of whatever you ordered. Save the box. Put stuff that Goodwill takes into the box. Print out a shipping label from the URL above. Slap it on the box. Send the box - off to Goodwill it goes, they process it, you even get a tax receipt.
Doesn't even have to be any special vendor's box!
It's sure a lot easier to declutter one wee cardboard shipping box at a time, it's basically no effort, and it recycles the box too :-)
http://givebackbox.com/works