This wonderful charitable effort supported by many of your favorite retailers will create a free prepaid shipping label for you to print that will route your items to the closest participating clothing donation charity (mine get sent to Goodwill). You just fill any sturdy shipping box you already have (like the box new clothes you bought online came in), attach the label, and either send it along with your USPS mail or drop it off at any USPS or UPS location. You can track your packages and get a donation tax receipt. It’s a great way to recycle old boxes, too.
Thred Up is a huge online consignment and thrift store,a and they’ve got a great setup available if you’d like to donate. Order their free donation kit, and they will send a prepaid bag to fill and leave for your mail carrier or drop off at any FedEx or USPS location. They’ll send along a donation to one of their partner charities and you will get a donation tax receipt.