Very little is known about Clinton’s 22 emails that are later deemed “top secret,” since all details about them have remained classified. However, it is known that one of them is sent sometime this year. A few details about just this one email are known because it will be included in a random selection of 40 emails that will get reviewed by State Department Inspector General Steve Linick in 2015.
After Linick decides the email should be top secret, the Central Intelligence Agency (CIA) and the National Geospatial-Intelligence Agency will perform a second review and confirm that the email should be top secret. That indicates the email contains information obtained from both CIA sources and US spy satellites. (The New York Times, 9/7/2015) (The New York Times, 2/29/2016)