Lawyer here. It isn't.
There is no question that former Secretary Clinton had authority to delete personal emails without agency supervision – she appropriately could have done so even if she were working on a government server. Under policies issue both by the National Archives and Records Administration (“NARA”) and the State Department, individual officers and employees are permitted and expected to exercise judgment to determine what constitutes a federal record. See NARA Bulletin 2014-06 ¶4 (Sept. 15, 2014) (“Currently, in many agencies, employees manage their own email accounts and apply their own understanding of Federal records management. This means that all employees are required to review each message, identify its value, and either delete it or move it to a recordkeeping system.”);3 Department of State Foreign Affairs Manual, 5 FAM 443.2(b) (“[t]he intention of this guidance is not to require the preservation of every E-mail message.”)