She chose to use a personal, unsecured mail server knowing that no classified material should be sent from or received by that server. As Secretary of State, she is the head of the State Department and it was her responsibility to make sure everyone at State understood that no email sent to her at that address should contain any classified information.
Whoa - as SoS she is an OCA. It was her responsibility to classify materials and she didn’t do it. Sedition . . .