I can believe IT chucked Lois Lerner's harddrive

The part that still needs explaining.  What are the requirements for record retention at IRS?  They ought to have some, in writing.  Lets see them. Do they back up desktops/laptops  over the network?  How often? Where are those backups? What does federal law require for record retention?  Is the IRS written policy in accordance with that law?  What does IRS use for an email server?  Microsoft Exchange?  Why does not the server archive all email? 
   If indeed, the IT people at IRS serviced Lois's computer and found the hard drive gone bad, they would replace it.  The old one would be chucked.  That part I can believe. 
   The part I have a lot of trouble believing is the idea that IRS email isn't routinely archived somewhere, just in case some bureaucrat needs a copy of something to prove a point. 
   I also have trouble believing that six of Lois Learner's partners in crime would all suffer total email loss at the same time. 
   I figure the Administration would rather take the heat from losing/refusing-to-furnish email than the heat they might get from a Lois email implicating the president in the stick-it-to-conservatives scandal.  That fact suggests that Lois had some pretty incriminating emails.