First-Class Mail is one of USPS's premium services. It is often as fast as Priority Mail with delivery estimated between 1-3 days.
This is a domestic service. Domestic mail is transported:
within, across, and between the United States.
from the United States to:
U.S. territories, Marshall Islands, Federal States of Micronesia.
U.S. military and diplomatic posts, and the United Nations, NY.
Large Envelope Flats is a special service within First-Class Mail. Flats are large envelopes that are smaller than 11.5" x 15", but larger than a regular envelope.
First-Class Mail rates are based on parcel weights and rate class.
Retail pricing is offered directly from the USPS at Post Office retail locations or USPS.com. It does not include discounts on postage prices like those received via ShipWorks.
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