Wolfgang's interpretation might be accurate, but I also don't think it matters. Regarding protecting data, none of it was safe, no matter on which server it was on.
As far as the actual email server scandal goes, regarding the mechanics of the server, only two things really matter.
1) That Hillary tried to withhold information from the National Archive, and thus history itself. Legal, illegal, doesn't matter. It was a shitty thing to do as a human, let alone a statesman, and should be instant disqualifier from holding any other office.
2) That if anyone else had been in a similar position, and done similar things, they would have been nailed, regardless of intent or technical legality. The DOJ would have concocted a dozen plausible-sounding charges, that even if they all seemed quite defensible individually, would still put the victim at risk of dozens of years of mandatory federal minimum sentences, and generally scare them into a plea bargain, especially if they didnt have access to a multi million dollar legal and PR team.
If memory serves, something similar actually happened to a former Clinton cabinet member, who accidentally left something innocuous yet classified in a book or folder that he took off-premise. The Clintons hung him out to dry, and he ended up becoming a convict. Even though his "breech" of security was, on the whole, much more innocuous and much less threatening to national security. But such is how it goes when you serve the Clintons: they don't have friends or colleagues, they have patsies and pawns.