How does the blue USPS box work? A while ago, I shipped a small

USPS Priority Mail: A Full Breakdown

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Is it okay to just put stamps on a large envelope (9x12', 12'x12') and put it in a mailbox, as long as it is under 13 ounces? Or does it have to

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Can you use cut-out USPS padded flat rate envelopes as bubble wrap to ship in a USPS box? Since you're still using the USPS service, I figure it's okay? - Quora

I accidentally, put a USPS regular letter with correct amount of stamps in a Fed-Ex box, will it still be mailed? - Quora

How many stamps do I need to ship a package to a P.O. box? - Quora

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