Deadly synthetic opioids are streaming into the United States amid a flood of mail that arrives unscreened from abroad every day, overwhelming the Postal Service and fueling the drug epidemic gripping much of the country, security experts and Massachusetts lawmakers say.

Nearly 1 million packages a day enter the country without any advance electronic information that might flag the presence of dangerous opioids such as fentanyl, much of which is manufactured in China, said Juliette Kayyem, a former assistant Homeland Security secretary.

An estimated 340 million pieces of mail each year pass unchecked through the Postal Service and US Customs without the prior electronic screening that was authorized by Congress 14 years ago but has yet to be fully implemented, Kayyem said..."There is a lot of money to be made," she said. In addition to opioids, security officials are concerned about hazardous materials and counterfeit goods that are slipping through.