(Justin Sullivan/Getty Images)

Federal authorities are investigating at least five suspicious letters sent in recent days to Senate and House district offices, and investigators are warning national news outlets to be on the lookout for similar letters.

The envelopes postmarked from a Portland, Ore. address contain a powdery substance that so far has tested harmless, according to officials.

Last fall as the U.S. Postal Service marked the 10th anniversary of the national anthrax mail attacks, The Federal Eye reported on steps taken since to secure the nation’s mail delivery system.

As we wrote at the time, the Postal Service now relies on both human checks and machine screenings to track suspicious mail. With tens of thousands of postal facilities to protect, the U.S. Postal Inspection Service has responded to more than 52,000 calls about suspicious mail since 2001, it said, and inspectors respond to about 10 calls daily. Most, they said, are false alarms.

Shift supervisors receive regular updates on evolving threats, and postal inspectors practice regularly with local law enforcement agencies in anticipation of an attack.

But mail was used as a weapon long before anthrax.

Historically, cases of dangerous mail are spawned by personal disputes between jilted lovers or feuding neighbors, inspectors said. In 1952, for example, a woman was arrested after she mailed a box of cyanide-laced Bon Bon Caramels to her estranged husband. He was suspicious and alerted authorities.

The USPS spends $101 million annually to screen every piece of first-class mail sent or received by U.S. households and mail sent to federal addresses in Washington.

To learn more about how the process works, click here.

Follow Ed O’Keefe on Twitter: @edatpost

Further reading:

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