Classified information isn't "classified" because someone stamps "classified" on it.
Classified information is sensitive information that could cause damage to the US if disseminated.
Hillary, as Secretary of State, was expected to be a determiner of what was "sensitive". She didn't need to see a stamp to know something was "classified".
Overtly or not doesn't matter. She had stuff she should not have had. And she managed it poorly. The hacking isn't central, the marking isn't central, her intent isn't central -- she mismanaged classified data. Pure and simple. She should be in jail and it should take a jury about 5 minutes to see it.
We've known this for years.
Everything at State is SENSITIVE UT UNCLASSIFIED - there is NO Unclassified, period.