Which category is NOT part of the four categories of International Mail?

The category that is considered NOT part of the four categories of International Mail is Standard International Mail. In the context of international shipping through USPS, the main categories established include Global Express Guaranteed, Priority Mail Express International, Priority Mail International, and First-Class Package International Service.

Understanding this framework is essential as it helps clarify the different levels of service available for international mailing, which vary in terms of delivery speed, tracking, and cost. Global Express Guaranteed (the fastest and most expensive option) and Priority Mail Express (another expedited option) represent premium services. First-Class is used primarily for smaller packages and letters that don't require the same level of service as the others. Therefore, Standard International Mail, while it might sound relevant, does not fit into the official classification system for international mail services as recognized by USPS.