I have a security clearance. I work for a large government agency. The views I express are my own and not necessarily of my agency's.

I have not committed a security violation, but I know others who have been written up for them.

Civilian employees are disciplined for security violations. It is extremely rare that they are jailed. These violations do happen. People leave briefcases in cabs and people forget to lock up at the end of the day, and sometimes people save a document on the wrong computer, etc. When this happens, a person receives either an "infraction" or a "violation" based on the severity of the offense. A violation might amount to a suspension without pay, or a dismissal, if one has committed violations in the past. Almost always, the employee is internally disciplined. If we prosecuted everyone who screwed up, nobody would want to work for us. If myself or one of my colleagues sent classified information over personal email, we would get a violation. I don't know what would happen if I ran my own email server; I don't have the same volume of email as a cabinet secretary! When people do get prosecuted, it is because they handed over classified information to an uncleared party on purpose

The FBI was correct not to prosecute Hillary Clinton. Similar cases have been handled internally, and her intent was to provide classified information to cleared parties, albeit on an uncleared system. The FBI followed precedent when investigating the case. Would Hillary Clinton have received a security violation if she were still Secretary of State? Yes. But since she isn't, it is a moot point.