US postal service offers Priority Mail shoe box
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The box measures 7-1/2 inches by 5-1/8 inches by 14-3/8 inches, is self sealing, and is available at no additional cost to Priority Mail users. 
For increased convenience, customers can also use Click-N-Ship - offered online through USPS.com - to print a shipping label with postage and use Carrier Pickup online notification to let their local Post Office know their package is ready for pickup when their letter carrier delivers their mail the following day. 
"Consumers are purchasing more clothing, shoes, and accessories than ever through the mail, and shoes are one of the hottest growing items in this category," said executive vice president and chief marketing officer Anita Bizzotto. "This packaging offers a quick, easy, and convenient solution for our customers in an important and growing market segment."