What document is necessary for international mailings?

For international mailings, a customs document is necessary as it provides essential information about the contents of the package, its value, and its destination. This document is crucial for customs authorities in the destination country to assess if any duties or taxes need to be applied and to ensure that the items comply with import regulations. Without a customs declaration, international shipments may experience significant delays or even be rejected at customs.

While the other documents mentioned have their own specific purposes—such as manifests for organizing shipments, proforma invoices for providing a preliminary bill of sale, and shipping labels for identifying the package and its recipient—they do not fulfill the essential role of declaring contents and value to customs officials in the context of international shipping. This makes the customs document indispensable for smooth international mail processing.