U.S. Customs authorities receive this transaction set from importers, freight forwarders, and carriers to document the contents and movement of cargo entering the United States through designated ports. The manifest provides customs officials with detailed information required for cargo clearance and border security compliance. Key structural elements include the M10 (Manifest Identifying Information) segment, which establishes the overall manifest details; the P4 segment within the P4 Loop, which specifies port-specific information for up to 20 ports; and the LX Loop, which accommodates up to 9,999 line items describing individual shipments, amendments, bills of lading, and cargo details. Supporting loops allow capture of shipper and consignee information through N1 segments, in-bond movement details via M12 segments, conveyance identifiers through VID segments, and hazardous material declarations using H1 and H2 segments.

Consider a practical example: an international freight forwarder like Apex Logistics prepares a customs manifest for a shipment arriving at the Port of Los Angeles from a supplier in Taiwan. The manifest uses the M10 segment to identify the specific cargo declaration, assigns the Port of Los Angeles in the P4 segment, and then creates line items in the LX Loop for each component—such as 500 units of computer circuit boards consigned to TechCorp Manufacturing, with shipper contact details captured in the N1 Loop. If hazardous materials are included, the H1 and H2 segments document their classification. U.S. Customs receives this manifest electronically before the vessel arrives, enabling pre-clearance processing and expedited release of compliant cargo upon port arrival.