What determines whether a letter can be dispatched to a specific country?

The ability to dispatch a letter to a specific country is primarily determined by international regulations. These regulations govern what can and cannot be sent internationally, including restrictions on certain items or requirements for documentation. Each country has its own set of regulations that define allowable mail items, customs requirements, and any prohibitions that may be in place.

Postage rates, service type, and weight play important roles in the mailing process and can influence the cost or service options available for sending mail. However, they do not dictate whether a letter can be dispatched to a particular country. It's the international regulations that ultimately guide the acceptance and processing of mail for different destinations. This ensures compliance with both U.S. postal standards and the receiving country's laws, which can vary widely.