United States Postal Service

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http://www.usps.gov/

Includes information about stamp releases, pictures of stamps available, searchable index for ZIP+4 codes, state and address abbreviations, preferred addressing methods, size standards for mail, postage rates for both domestic and international mail delivery, history of the USPS, news releases, calendar of events, and other postal-related information. The business section of this Web site includes information both for the mailing needs of businesses and for the business needs of the USPS. Businesses wishing to sell products to the USPS will find a purchasing manual and information about selling products to the USPS at this Web site.