Which type of mail consists of items sent within the United States?

The correct answer is domestic mail, as it refers specifically to items sent within the boundaries of the United States. Domestic mail encompasses various services, including standard letters and packages sent from one location to another within the U.S. This type of mail is crucial for everyday communication and shipping needs among residents and businesses within the country.

International mail, on the other hand, pertains to items being sent to or received from countries outside of the United States, which is why it does not fit the criteria of this question. Priority mail and express mail are specific services offered by postal services that prioritize speed and delivery time for domestic packages but still fall under the broader category of domestic mail rather than defining it. Therefore, while all of these options relate to mail services, domestic mail is the one that specifically and accurately describes items sent within the United States.