I was just reading this as reported by ABC news 2 days ago:

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"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.

Clinton has not said why she requested the book, but it includes some
advice that is particularly interesting in light of the controversy over
her unconventional email arrangement at the State Department and her
decision to delete tens of thousands of emails she deemed to be purely
personal.

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.”

“Some people are hoarders, some are checkers,” the authors write. “The
main thing to consider is that once you do decide to delete, it’s like
taking the garbage from your kitchen and putting it in your hallway.
It’s still there.”

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.”

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The ABC article also include an image of the email reply to Hillary from
Cheryl Mills (State staff member) This is the content:

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From: Mills, Cheryl D
Sent: Tuesday, December 1, 2009 8:25 PM
To: H
Subject: May I borrow

Will bring tomorrow

--- Original Message ---

From: H
Sent: Tue Dec 01 19:17:57 2009
Subject: May I borrow

SEND by David Shipley?

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and thus, the coverup began.