Actually, no. She violated Department of State policy by using an unauthorized mail server for official communications. Employees of the State Department violated information security regulations by installing classified documents on an unclassified State Department network, and forwarding them to her account on the unauthorized server. Neither was in itself a crime. Creating or storing classified documents on the unclassified network was a regulatory violation punishable by administrative action, in egregious cases including suspension or dismissal. I’m not sure about the mail server; that’s an issue which never came up while I was responsible for information security during my tenure with the federal government. (I had access to both the classified and unclassified networks managed by the State Department, and worked with members of the Department’s IT staff.)
The discussion about sending classified material improperly and violating procedures for handling classified information was a fig leaf to cover up the real reason. Hillary Clinton used her private server to communicate with leaders and other foreigners about contributions to the Clinton Foundation and other payments that she wouldn't be able to hide if she used the State Department's classified server. It would belong to the government and those email would be memorialized in history.
Her argument that the 30,000 private emails she deleted were about recipes she discussed with in-laws and other such private stuff was a subterfuge. She needed her own server so she could scrub all the emails between the Clintons and the people who gave the Clintons money apparently in exchange for favors. The security aspect was just a distraction used to keep the focus off the real reason for the private servers. Unfortunately, the press wanted her to be president so went along with the subterfuge. They didn't do their job.
