The U.S. Postal Service and its internal watchdog plan to review whether or not some of the agency's employees may have violated federal policies by using their government email on the infidelity website Ashley Madison.
"We are looking into this matter and will follow our existing administrative process if misconduct is identified," U.S. Postal Service spokesman Dave Partenheimer said in a statement.
Cyber security experts said data dumps on Tuesday and Thursday by a group calling itself Impact Team appeared to be authentic, exposing customer information that included government email addresses.
Some of those addresses posted on pastebin.com are pegged to the Postal Service. Reuters could not verify the authenticity of the information posted on the website.
A spokeswoman for the Postal Service's inspector general said her office is also evaluating whether further investigation is warranted, and noted that more information is needed before determining if any violations may have occurred.
She added that the Postal Service does have a limited use policy which permits employees to use work email for personal reasons as long as it does not adversely affect productivity, interfere with the mission of the postal service or violate ethics standards.