In a normal world that would not matter. Whether the emails were stamped and controlled is irrelevant.
The information itself was classified.
To get TS/SCI you have to be thoroughly briefed, when you leave the job, thoroughly debriefed.
You also sign an official acknowledgement and are warned that unauthorized disclosure will result in prosecution under US Code xyz, punishable by up to 50 years in prison.
Purposeful release to a foreign government (spying) is punishable by up to death.
Worth repeating from your post:
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To get TS/SCI you have to be thoroughly briefed, when you leave the job, thoroughly debriefed.
You also sign an official acknowledgement and are warned that unauthorized disclosure will result in prosecution under US Code xyz, punishable by up to 50 years in prison.
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And you can be assured that Hillary signed many such documents while she was SoS.