@Olivier5,
I am not playing with words, she is not the subject of the investigation, in the FBI own words not mine. She has not been charged with any crime. Perhaps they are looking at security breaches which happened in her emails. (The same happened with Pentagon and congress and the state department, so using those servers wouldn't have been any safer.)In other words, it wasn't a crime for her to use a private server for her emails, hence Clinton not being the subject of the investigation.