https://techcrunch.com/2018/11/26/the-us-postal-service-exposed-data-of-60-million-users/

A broken US Postal Service API exposed from over 60 million users and allowed a researcher to pull millions of rows of data by sending wildcard requests to the server. The resulting security hole has been patched after repeated requests to the USPS.

The USPS service, called InformedDelivery, allows you to view your mail before it arrives at your home and offered an API to allow users to connect their mail to specialized services like CRMs. We profiled in the service in 2017.