Which type of mail includes items sent within the US, APO, FPO, UN, and its territories?

The category that encompasses items sent within the US, which includes delivery to military addresses (APO, FPO), United Nations addresses (UN), and its territories, is known as domestic mail. This classification specifically refers to all mail that is sent within the borders of the United States, making it distinct from international mail that is sent outside of the U.S. borders.

Domestic mail is a broad category that includes various types of mail services, such as first-class mail, priority mail, and standard mail, all intended for delivery within the country. Understanding this distinction is crucial because it helps in correctly addressing and processing mail according to its destination.

Other mail types listed, like express mail, refers specifically to expedited shipping services, while bulk mail pertains to large quantities of mail sent at a discounted rate. Thus, domestic mail is the most accurate choice given the context provided in the question.