what is express priority mail
Priority Mail Express Flat Rate is a fast, overnight shipping service provided by the U.S. Postal Service (USPS) that features one low flat rate for the delivery of packages or envelopes.sing Priority Mail Express Flat Rate is very simple. As long as your package is not heavier than 70lbs., you will not need to weigh it. When preparing to ship with Priority Mail Express Flat Rate, you can order the free envelopes or boxes through the USPS website or pick these up at the Post Office.