The U.S. Postal Service (USPS) will implement new rates ...

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Jan 27, 2019 · First-Class Mail is a service that delivers envelopes weighing up to 3.5 ounces and flats up to 13 ounces. This service is ideal and cost-effective for letters, bills, large envelopes, and postcards. This mail class offers delivery between one and three days within the U.S.

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