1). Use of private email allowed her to control what emails were made available. We now know those servers were wiped clean and emails are missing. Violation.
2). Allowing public access to emails. See point 1, a private email server allows that person what is made available and what isn't.
3). Same as the other two, National Archives is where all gov't emails eventually end up. Having a private server, once again, allows the user to control what emails are readily accessible.
4). It's illegal to store classified information on a private server. But the deletion of 30K + emails makes it impossible to know if she did or didn't.
And then there is this:
"Electronic records show Peter Strzok, who led the investigation of Hillary Clinton's private email server as the No. 2 official in the counterintelligence division, changed Comey's earlier draft language describing Clinton's actions as "grossly negligent" to "extremely careless," the sources said."
Do you know why? It's because "grossly negligent" is still breaking the law.
https://www.cnn.com/2017/12/04/politics/peter-strzok-james-comey/index.html