Shortly before she was sworn in as secretary of state in 2009, Hillary Clinton set up an email server at her home in Chappaqua, New York.
She then relied on this server, home to the email address hdr22@clintonemail.com, for all her electronic correspondence - both work-related and personal - during her four years in office.
She also reportedly set up email addresses on the server for her long-time aide, Huma Abedin, and State Department Chief of Staff Cheryl Mills.
She did not use, or even activate, a state.gov email account, which would have been hosted on servers owned and managed by the US government.
Mrs Clinton's email system became a national story the first week of March 2015, when the New York Times ran a front-page article on the subject.
The article said that the system "may have violated federal requirements" and was "alarming" to current and former government archive officials.
According to Mrs Clinton, the primary reason she set up her own email was for "convenience".
During a press conference at the UN, she said that she preferred to carry only one smartphone with one email address, rather than have two devices - one for work and one for personal affairs.
Source BBC