FBI agents said they recovered 17,448 "unique work-related and personal" emails from Hillary Clinton's private server that were not provided by her legal team.

The revelation came in notes released Friday by the FBI related to the investigation of Clinton's email system.

Agents said 81 email chains discovered in the course of their year-long probe should have been considered classified at the time they were written, contrary to Clinton's claims that everything sensitive was retroactively classified.

In addition, three emails bearing "confidential" classified markings were discovered on her server. The Democratic nominee said she assumed the "C" marking was a way to sort paragraphs alphabetically.

Clinton accessed her emails on 13 different mobile devices, raising questions about her March 2015 claim that she used a private server to consolidate all her communications on just one device.

Read the full FBI notes on the Clinton email probe here.

Hillary Clinton's Email Controversy Graphiq

