First of all, get your mind clear on this one thought: What really matters is not the illegality of Hillary's schlock, homebrew e-mail server, nor is it the classified information that was jeopardized because it passed through said server. That matters, but not as much as the thing that really matters.
What really matters is the pay-for-play, bribery corruption of the Clinton Foundation. The e-mail server was set up to prevent Congress, the media and the public from learning what was really going on with the Clinton Foundation. The fact that the server was discovered, and that we now know classified information was compromised because of it, is flitting around the edges.
Hillary knew she was playing a dangerous game handling classified information in this way. (So did Obama, by the way.) She did it anyway because the security of classified information was nowhere near as important to her as making sure no one ever knew how brazenly the Clinton Foundation was trading influence for cash.