The basic premise of the postal mailability statutes is that anything “which may kill or injure another, or injure the mails or other property...” is nonmailable. Several statutory exceptions to this rule permit mailings of otherwise nonmailable matter under specified conditions. Statutory exceptions apply to live scorpions, poisonous drugs and medicines, poisons for scientific use, switchblade knives, firearms, motor vehicle master keys, locksmithing devices, and abortive and contraceptive devices. The statutes also provide that the USPS may, by regulation, permit the mailing, under required conditions of preparation and packing, of potentially harmful matter not “outwardly or of [its] own force dangerous or injurious to life, health, or property.” The regulations in this publication summarize the statutory prohibitions and exceptions; detail the mailability standards that apply to perishable, hazardous, and restricted matter; contain information on the mailability of specific hazardous materials; and describe the conditions of preparation and packaging under which the USPS accepts for mailing potentially harmful matter that is otherwise nonmailable.
Restricted matter is an article or substance prohibited or limited by Title 18, U.S. Code (liquors, abortive and contraceptive devices, odd-shaped items in envelopes, motor vehicle master keys, and locksmithing devices). It also includes matter not otherwise described in this publication that is restricted by 18 U.S.C. 1716(a) because it may, under conditions encountered in the mail, be injurious to life, health, or property (obnoxious odors, liquids, powders, and battery-powered devices).
Except as provided in this publication, any article, composition, or material is nonmailable if it can kill or injure another or injure the mail or other property. Harmful matter includes, but is not limited to:
- All types and classes of poisons, including controlled substances.
- All poisonous animals except scorpions mailed for medical research purposes or for the manufacture of anti-venom (or antivenin or antivenene); all poisonous insects; all poisonous reptiles; and all types of snakes, turtles, and spiders.
- All disease germs or scabs.
- All explosives, flammable material, infernal machines, and mechanical, chemical, or other devices or compositions that may ignite or explode.
Harmful matter also includes regulated hazardous materials that are likely to harm USPS employees or to destroy, deface, or otherwise damage mail or postal equipment. This includes materials such as caustic poisons (acids and alkalis), oxidizers, or highly flammable liquids, gases, or solids; or materials that are likely, under conditions incident to transportation, to cause fires through friction, absorption of moisture, or spontaneous chemical changes or from retained heat from manufacturing or processing, including explosives or containers previously used for shipping high explosives with a liquid ingredient (such as dynamite), ammunition, fireworks, radioactive materials, matches, or articles emitting obnoxious odors.
Matter is nonmailable also when it cannot be delivered because of an illegible, incorrect, or insufficient address, or when it does not meet USPS standards for mail preparation, classification, postage prices, size, or weight.