At the same time, the cost of some Priority Mail shipping materials, including flat-rate envelopes and boxes, will go down. Using a flat-rate box or envelope lets you send a package of up to 70 ...

The cost of Priority Mail Express Flat Rate Envelope will be $30.45 pending approval, according to USPS. Costs for the USPS Ground Advantage will vary on the cost of the country it's being mailed ...

While these are a little more pricey than the 66 cents it costs to stick a stamp on a letter, Priority Mail sent domestically includes $100 of insurance. The envelopes also look less appealing ...

Newly designed priority mail boxes and envelopes are already appearing at high-volume post offices, and customers should see them nationwide within the next couple of weeks, Manabe said.