You may legally carry or mail any amount of money you want into or out of the United States, but if it is more than $10,000 at one time, you better first report it to U.S. Customs and Border Protection. Otherwise, you risk U.S. Customs taking it from you, and never getting it back. Why? Because your failure to report the international transportation of money is a violation of the Currency and Foreign Transaction Reporting Act.
All too often, I am contacted by a distraught American ciitizen or resident returning from a trip overseas, or a foreign visitor to the United States, who was unaware of the laws regarding currency reporting. The person was asked by a U.S. Customs officer upon arrival at the international airport if he or she was carrying over $10,000. When the passenger honestly answer "yes", or the U.S. Customs officer believes the passenger may be lying about the amount of money being transported, the passenger and his or her luggage are examined. If over $10,000 in monetary instruments, including travelers checks and U.S. or foreign money, is discovered, and the required form, FINCEN Form 105, has not been filed with U.S. Customs, all of the money is likely to be seized on the spot by U.S. Customs.
A formal Seizure Notice will eventualy be issued by U.S. Customs to the passenger, and the passenger may hire a customs attorney to pursue the administrative petition process to get the money (or most of it) back. Proof of the legitimate source of the money and proof of the legitimate intended use of the money are required in communicating with Customs. Eventually, after several months, Customs may return typically 90% of the money.
It is an expensive mistake to not report to U.S. Customs when either carrying, mailing, or receiving over $10,000 internationally. Please read U.S. Customs and Border Protection's "Currrency Reporting" flyer and look at the FINCEN Form 105 and its instructions before attempting to transport over $10,000. There are no customs duties, taxes or other fees paid to U.S. Customs for the international transportation of the money; it is merely a reporting requirement to U.S. Customs.