I have two different Priority Mail medium size boxes from the USPS. One says "Flat Rate" and the other says "Domestic or International Shipping." For domestic shipping, if I want to send something Priority Mail in a medium box but don't want to use the flat rate of $16+, is the other box for calculated rate shipping? I've been trying for two days to get through to the post office to ask but am unable to get a person. Thanks. I hope my question is clear.
