September 22, 2015: Clinton’s emails were improperly secured up until August 2015.

After it became clear by May 2015 that some of Clinton’s emails contained classified information, the security of the email copies possessed by Clinton’s lawyer David Kendall became an issue. In July 2015, State Department officials installed a special safe in Kendall’s office to store them.
However, on this day, Assistant Secretary of State Julia Frifield writes to Senate Judiciary Committee Chair Charles Grassley (R) that “while the safe was suitable for up to (top secret) information, it was not approved for TS/SCI material.” “TS/SCI” stands for “top secret, sensitive compartmented information.” Top secret information and above, such as TS/SCI, must be kept in a specially built secure room known as a SCIF [sensitive compartmented information facility]. Frifield argues that no one in the department knew Clinton’s emails contained such highly classified information.
The issue was resolved in August 2015 when the FBI took away Kendall’s copies of the emails. (The Associated Press, 9/28/2015)