Flashback: Hillary Clinton's emails row
What exactly did Hillary Clinton do?
From 2009 to 2013, Ms Clinton used a personal server and email address - firstname.lastname@example.org - during her four years as secretary of state. She also reportedly set up addresses for her aide, Huma Abedin, and State Department chief of staff Cheryl Mills.
She did not activate or use an official state.gov email account. That account would have been hosted on secure US government servers.
Why did she use a personal email address for official correspondence?
During a press conference at the UN, Ms Clinton said that she preferred to carry just one smartphone with one email address, rather than have separate devices (one for work, one for personal emails). At the time, government-issued Blackberry phones were reportedly unable to access multiple email accounts.
Why was this controversial?
Critics claim there was a security risk if restricted government business was sent over personal email servers (Ms Clinton says no information in her emails was marked classified at the time she sent or received them).
They also say Ms Clinton could skirt around freedom of information requests, with sole control of what information was handed over to interested parties, such as the congressional committee investigating 2012's Benghazi consulate attack in Libya.
Was it illegal?
It's a grey area. Federal law during Ms Clinton's tenure called for the archiving of such private email records when used for government work, but did not set out clear guidance or punishments for violations. Rules were subsequently tightened after she left office.
In 2011, when Ms Clinton was secretary of state, a cable from her office sent to all employees advised them to avoid conducting any official business on their private email accounts because of targeting by unspecified "online adversaries".
In 2016, the FBI concluded that it had found no evidence of criminal wrongdoing.
How many emails were involved?
Ms Clinton says she sent or received 62,320 emails while secretary of state. Her lawyers say 30,490 of those were official and they've been turned over to the State Department. Ms Clinton said the remaining emails were about private matters, such as her daughter's wedding and her mother's funeral.