I don't think that the email controversy mattered very much for the 2016 election: I think many voters simply didn't like Clinton, and the email issue serve to

I don't think that the email controversy mattered very much for the 2016 election: I think many voters simply didn't like Clinton, and the email issue serve to support preexisting beliefs rather than swaying anyone. And yes, jailing her would be rather extreme step, as the practice does appear to be rather common, if not exactly "best", like you describe it (there were explicit laws against precisely that). However, this is just another example of the fact that among the elites, legal system is just an extension of politics, a tool used to achieve specific political goals. That does not give it much legitimacy in the eyes of the common folk, who see that they are simply lied to when they are told about "equality under the law".