Each year, the U.S. Postal Service (USPS) processes billions of pieces of mail—and photographs every single one.

Like other federal agencies that have been exposed for their secretive surveillance programs, the Postal Service has quietly been capturing the information on letters and packages sent throughout the country.

The Mail Isolation Control and Tracking program was implemented following the 2001 Anthrax attacks that killed five people, including two postal workers. It involves computers used by the USPS that photograph the exterior of all paper mail processed in the U.S.

Last year, the Postal Service handled about 160 billion pieces of mail.

The secretive program became public during the Federal Bureau of Investigation’s work to determine who sent ricin-laced letters to President Barack Obama and New York City Mayor Michael Bloomberg.

The Mail Isolation Control and Tracking program allows the Postal Service to retrace the path of mail at the request of law enforcement.

Before that, the USPS used what’s called “mail covers” that entailed selectively photocopying the outside of mail belonging to those under suspicion or deemed a potential threat by federal or local law enforcement. Mail cover requests, which still average more than 15,000 a year, are used to investigate a variety of crimes, including prostitution, drug smuggling, fraud and corruption.

However, the program, which does not require the approval of a judge, can be abused, as in the case of Maricopa County, Arizona, Sheriff Joe Arpaio, who, in May 2012, was ordered to pay almost $1 million to County Supervisor Mary Rose Wilcox after a judge ruled that his mail cover request was politically motivated with no connection to a crime investigation.

“In the past, mail covers were used when you had a reason to suspect someone of a crime,” Mark D. Rasch, who started a computer crimes unit in the fraud section of the criminal division of the Justice Department and worked on several fraud cases using mail covers, told The New York Times. “Now it seems to be, ‘Let’s record everyone’s mail so in the future we might go back and see who you were communicating with.’ Essentially you’ve added mail covers on millions of Americans.”

-Noel Brinkerhoff

To Learn More:

U.S. Postal Service Logging All Mail for Law Enforcement (by Ron Nixon, New York Times)

Ricin Suspect Was Tracked Via Mail Scanners (The Smoking Gun)