What type of mail requires a customs declaration form when shipped internationally?

When shipping items internationally, all international shipments require a customs declaration form. This form is essential as it provides customs authorities with information about the contents of the package, its value, and the purpose of the shipment. The customs declaration helps facilitate the processing of the items through customs and ensures that duties and taxes are appropriately assessed where applicable.

Every piece of mail, whether it be packages, letters, or large envelopes, must have this form if it crosses international borders. This requirement is vital regardless of the contents or the weight of the shipment. Thus, stating that all international shipments necessitate a customs declaration accurately reflects the regulations governing international mail.