The last batch of Hillary Clinton emails released by the State Department included one from Clinton asking to borrow a book called “Send: Why People Email So Badly and How to Do It Better,” by David Shipley and Will Schwalbe.

The copy that ABC downloaded for $9.99 had some interesting revelations.

Take, for example, Chapter Six: “The Email That Can Land You In Jail.” The chapter includes a section entitled “How to Delete Something So It Stays Deleted.”

The chapter advised that to truly delete emails may require a special rewriting program “to make sure that it’s not just elsewhere on the drive but has in fact been written over sixteen or twenty times and rendered undefinable.”

But Shipley and Schwalbe warn that deleting emails could lead to future legal troubles.

On page 215, the authors list “Stupid (and Real) Email Phrases That Wound Up in Court.” Number one on the list? “DELETE THIS EMAIL!’ Later, on page 226, the writers warn, “If you’re issued a subpoena, your deletion binge will only make you look guilty.”