I’m very confused:
If she wiped her server clean, how does anyone know there were classified emails?
From how I understand it, all the government needs is the MAC address, which is hardwired to the NIC. From that, they can piece together emails that left that device and also emails that pointed towards that device.
In other words, in order to truly destroy your emails, it's not enough to delete them off your own computer. You also need to delete them off all the computers that ever sent you mail and all the computers that you sent mail to.