it seems she had to have intent, and Comey made the decision she didn't.
Comey said the Justice Department shouldn’t prosecute Clinton because there isn’t enough evidence that she intentionally mishandled classified information. FBI investigators didn’t find vast quantities of exposed classified material, and they also did not turn up evidence that Clinton intended to be disloyal to the United States or that she intended to obstruct justice.
When I worked with nuclear weapons in the late 1950s, the first thing we were told was "never discuss your work outside of the work place. If caught, the fine was ten years in prison and $10,000. $10k in the 50s was more money than most people had.
I'm sure any secretary of state was given similar instruction. That's where I'm having difficulty. Even if she didn't have intent, she should have known that exposing confidential information to hackers should not require the brains of a computer genius. News about hacking of government departments have been common knowledge.