The presumptive Democratic nominee has repeatedly denied she sent or received classified information using her private account while she was in the role.
The scandal has not dampened President Barack Obama's endorsement of her.
The FBI has announced US Democratic presidential candidate Hillary Clinton will not face charges for using her private email account to send emails as Secretary of State.
The issue has dogged Ms Clinton throughout her campaign, with polls continuously showing strong public doubt over her honesty and trustworthiness.
FBI director James Comey says, while there is evidence she used her personal server to send and receive classified information, there is no proof she set out to break any laws.
"Although we did not find clear evidence that Secretary Clinton or her colleagues intended to violate laws governing the handling of classified information, there is evidence that they were extremely careless in their handling of very sensitive, highly classified information. There is evidence to support a conclusion that any reasonable person in Secretary Clinton's position, or in the position of those with whom she was corresponding about those matters, should have known that an unclassified system was no place for that conversation."
While the Department of Justice actually has the final say on the matter, it is unlikely to go against the FBI recommendation.
Ms Clinton's Republican rival, businessman Donald Trump, has released a statement accusing investigators of failing to hold her to account.
He has again maintained the scandal should exclude her from the race for the White House.
The findings have riled the State Department in a different way, with spokesman John Kirby dismissing the FBI's view that the department has a careless approach to classified material.
"I do want to address the claim about a lax environment or culture when it comes to handling classified information. And I would just say -- and I'm comfortable commenting on that, because, as the director himself said, that was not part of their investigation -- their assessment of a lax environment or culture, we don't share that assessment of our institution. That said, and I've said this many times before, we're always looking for ways to improve. We're going to continue to look for ways to improve."
The Republicans are also pushing for an independent inquiry into the matter, saying they do not believe the Justice Department is impartial enough.
But the issue has not stopped President Barack Obama from enthusiastically endorsing Ms Clinton in his first appearance with her at a rally in the state of North Carolina.
He says she is ready to make the decisions a president faces.
"I can tell you this: Hillary Clinton has been tested. She has seen up close what's involved in making those decisions. She has participated in the meetings in which those decisions have been made. She's seen the consequences of things working well and things not working well. And there has never been any man or woman more qualified for this office than Hillary Clinton. And I want you to help elect her to be the next president of the United States of America."
