domestic intel
Postal Service photographs and logs every piece of mail or package logs every sender and recipient. Optical charachter recognition, etc.
You have a file. So do I and so does everyone else.
The data is available to LEOs and intel agencies like license plate scanner data.
Fills the gap not covered by electronic eavesdropping or FISA on email, texts, calls, geolocation.
"Postal Service Confirms Photographing All U.S. Mail"
https://web.archive.org/web/20130803093206/https://www.nytimes.com/2013/08/03/us/postal-service-confirms-photographing-all-us-mail.html