What does IMM primarily govern?

The correct answer is that IMM primarily governs international mail. The International Mail Manual (IMM) provides guidelines and regulations that outline how international mail should be processed, including requirements for packaging, labeling, and customs documentation. Its primary aim is to facilitate the smooth transit of mail across borders, ensuring compliance with both domestic postal regulations and the international agreements established between countries. This comprehensive framework covers various aspects of international mailing, including prohibited items, customs duties, and international mailing options, thereby serving as an essential resource for postal services and customers engaging in international shipping.

The other options refer to areas that may involve different sets of guidelines or policies. Domestic mail services, postal policies, and postal forms are typically governed by other manuals or regulations that focus on domestic operations rather than the specifics of international mailing standards.