As a former member of the intelligence community I felt a deep shadow fall over me as I read about Hillary Clinton's use of an outside email service instead of the more secure and private State Department system. She did this for obvious reasons, to keep her communications out of official channels and away from the prying eyes of her political enemies (the Republicans...). One might sympathize with a politician in her situation.
However, the Secretary of State of the United States of America is the number two intelligence target IN THE WORLD, behind only her boss, the President. To tap into her communications guarantees lavish rewards and promotions to the intelligence team who does it. All eyes are on her, like vultures, waiting. Yes, it really works this way.
An email system such as the one described is considered "easy pickings." After seeing the details in the press, my first conclusion is this:
Russians and the Chinese were reading her emails. In real time.
I'm not saying maybe or perhaps.
The Russians and Chinese have sophisticated intelligence services, with sophisticated spotting, assessing, targeting capabilities. They have thousands of people who work these issues. Ms. Clinton may say that she didn't talk about classified matters, and she may think this is correct. But any intelligence professional knows its impossible to "talk around" a topic effectively (despite what you might see in spy movies...). With a high value target like Ms. Clinton, an intel service will have teams of analysts and psychologists analyzing every word she says, with absolutely clear context.