19 CFR 145.0: Scope.

(a) The provisions of this part apply only to mail subject to Customs examination as set forth in § 145.2. This part contains regulations pertaining specifically to the importation of merchandise through the mail but does not contain all the regulations applicable to mail importations. Importations by mail are subject to the same requirements and restrictions as importations by any other means, except where more specific procedures for mail importations are set forth in this part. The fee applicable to each item of dutiable mail (other than Inbound Express Mail Service (EMS) items) for which Customs prepares documentation, and the fee applicable to all EMS items, is set forth in § 24.22 of this chapter.

(b) This part also contains regulations requiring the United States Postal Service (USPS) to transmit certain advance electronic data (AED) to U.S. Customs and Border Protection (CBP) for certain inbound international mail shipments as set forth in subpart G of this part.