Postmaster General John Potter told a news conference the nine-month operation stopped more than a half million fake checks from being mailed to U.S. victims and involved cooperation with authorities in Nigeria, Netherlands, England and Canada.
Potter said there is a common pattern to the various ruses.
"Scammers contact victims online or through the mail and send them checks or money orders. They then ask that some portion of the money be wired back to them," Potter said. "The old adage still holds true -- if someone offers you a deal that sounds too good to be true, it probably is."
He said the crackdown had netted more than $2.1 billion in counterfeit checks bound for the United States.
A USPS news release said consumers who suspect they are being targeted should contact the Postal Inspection Service at 800-372-8347.