The IRS claims they can recover Lois Lerner's email from 2011 and earlier because Lerner's hard drive crashed and they only backed up for 6 months and then reused the data tapes. That seems to be a stupid explanation, but for the sake of this discussion, let's stretch credibility and assume the IRS and Lerner are completely truthful.
Prior to the eruption of the IRS controversy last spring, the IRS had a policy of backing up the data on its email server (which runs Microsoft Outlook) every day. It kept a backup of the records for six months on digital tape, according to a letter sent from the IRS to Sens. Ron Wyden (D-Ore.) and Orrin Hatch (R-Utah). After six months, the IRS would reuse those tapes for newer backups. So when Congressional committees began requesting emails from the agency, its records only went back to late 2012.
The IRS has described the missing e-mails as dating from 2009 to mid-2011. At that point, the agency says its computer system had a strict limit for the e-mail capacity of each employee’s account. If a worker went above that capacity, they had to either move e-mails to their hard drive or delete them. When Lois Lerner’s hard drive crashed in 2011, the agency states, her saved e-mails were lost from her account and computer.
The IRS provided e-mails from 2011 in which Lerner asked IT support staff for help with her broken hard drive and missing e-mails. The agency says it has recovered 24,000 of those e-mails by searching the accounts of 83 other IRS employees who corresponded with Lerner.
According to these emails, Lerner and the IRS took almost heroic efforts to recover Lerner's files.