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Mailing Standards of the United States Postal Service,
International Mail Manual >
7 Treatment of Inbound Mail > 720 Plant and Animal Quarantine Inspection
All packages that contain plants, plant products, soil, plant pests, plant material used for packing, animals, and animal products and byproducts, including meats, are subject to agricultural quarantine inspection by the U.S. Department of Agriculture (see DMM 601).