Publication 52, Hazardous, Restricted, and Perishable Mail > 1 Introduction > 12 Scope
The scope of this publication extends to all articles and materials that are nonmailable because they may harm people or property or that have mailing restrictions imposed upon them by the regulations of other governmental agencies.
Under 18 U.S.C. 1716 all matter that is outwardly or of its own force dangerous or injurious to life, health, or property is nonmailable. The knowing deposit of such matter in the mail is a crime punishable by fine, imprisonment, or other penalty. However, certain hazardous materials and otherwise restricted and perishable matter may be mailed under the conditions permitted in this publication.