It's also important to note that the data may not be able to be recovered. One great block of instruction from an attorney over the years relayed that the best answer in a digital forensics investigation is "it depends"... and this situation very much depends on the physical state of the hard drive, the manner in which the sectors went bad and other factors such as the care of the hard drive, storage methods, recovery methods, time, etc. Politicians and lawyers don't generally like the answer "it depends" because it's not definitive, but increasingly in life, things aren't as definitive as we'd like them to be. It may appear dubious that such a prominent figure in the IRS was archiving her emails locally (on the desktop computer) and not on a server. In fact, in our research to date, we haven't seen much mention of a server archive, only temporary storage. Regardless, it is entirely possible that the emails Congress is seeking may either not exist or not be able to be recovered (fully)... that is simple scientific fact.
Patrick J. Siewert
Owner, Lead Forensic Examiner
Pro Digital Forensic Consulting