If you mail money or a money order as part of a dishonest scheme or send cash out of the continental U.S., you may be prosecuted under the federal mail fraud law. The law covers any intentional activity that is designed to defraud another party through the mail. The mailed items are not required to carry any misrepresentation or falsifications themselves if they can be linked to a larger plan with fraudulent intent. Federal mail fraud laws apply to private carriers such as UPS and Federal Express because they carry parcels across state lines. Many states also have their own laws against mail fraud.

The same federal law prohibits the use of the postal system for chain letters and foreign lotteries. A chain letter is any mass mailing promising monetary payment if the recipient continues the chain by forwarding the letter to several friends or family members. The number of recipients grows exponentially to become a Ponzi scheme, meaning only the first few mailers have a chance to earn any money. Only state-operated lotteries may send lottery tickets or related materials through the mail. An individual may not mail money to purchase tickets or shares in a foreign lottery. This law is designed to protect postal customers from foreign scams that target U.S. addresses.

While it is not illegal to mail money or money orders within the United States, it is still not a good idea to send large amounts of cash this way. Cash may easily be destroyed, lost or stolen before reaching the recipient. You will have no recourse for a loss if you did not purchase insurance prior to sending the package. It is better to send a check or money order because you can stop payment and recover your funds. If you absolutely must send cash, conceal it with paper so the envelope does not attract thieves.