31 CFR § 560.521 - Diplomatic pouches.
The following transactions are authorized:
(b) The exportation, reexportation, sale, or supply, directly or indirectly, from the United States or by a U.S. person, wherever located, of any goods or technology to a third-country government, or to its contractors or agents, for shipment to Iran via a diplomatic pouch. To the extent necessary, this section also authorizes the shipment of such goods or technology by the third-country government to Iran via a diplomatic pouch.
The exportation or reexportation of certain U.S.-origin goods or technology to a third-country government, or to its contractors or agents, may require authorization by the U.S. Department of Commerce under the Export Administration Regulations (15 CFR parts 730 through 774).