> Has there been anything like this before? If I work for the government and forward confidential and secret emails through to a server I'm running myself I imagine I'd have criminal proceedings against me.

Unlikely. You would lose your job for sure, but typically for a criminal prosecution to result there has to be an element of willful unauthorized disclosure of classified info, or very high impact of the disclosure of classified info.

In practice this means that the people who get prosecuted have almost always been people intentionally sharing secrets with foreign entities (spying).

I only know of one case where charges were brought against someone who was not doing that. It was when the feds retaliated against Thomas Drake for whistleblowing against the NSA. Even then the charges got dropped.