Hillary Clinton isn't the only State Department official to use a private email account for official, and sensitive, government business. The Daily Mail reports that Caroline Kennedy, the US Ambassador to Japan, has also been caught using a private account.:

The State Department's Office of Inspector General says it has identified instances where emails labeled 'sensitive but unclassified' were sent from or received by personal email accounts.

It says department employees are expected to use approved, secure methods to transmit sensitive but unclassified information when available and practical. The report on the embassy's operations was conducted between January and March.

Kennedy, the daughter of the late President John F. Kennedy, was named Ambassador to Japan in 2013 after helping to campaign for Barack Obama in 2008 and 2012, including serving on his vice-presidential search committee.

The use of private emails for government businesses, especially diplomatic business, is frowned upon and violates government policy. The practice raises security questions over who could potentially read the emails and access the information contained therein.

The use of a private email account and server by Hillary Clinton, including potentially handling top-secret intelligence info on the private server, had dogged the Democratic presidential hopefuls campaign and prompted questions in Washington about proper security protocols.