To find something, you can turn on the lights or turn up the heat. In the case of Lerner's missing emails, heat seems to have been more effective than light. Under extreme heat IRS has just admitted that maybe Lois' emails might be available after all.
In actual fact, the IRS excuses about crashed hard drives are BS, even though the newsies have fallen for them. The emails all travel over the office local area network (LAN) and thru central email server computers. Which are probably running Microsoft Exchange Those servers can keep a complete record of every email ever sent, neatly sorted by sender, receivers and date. In the IRS, which might need an old email to either prosecute tax payers or defend itself in court or in front of Congress, it is inconceivable not to have central archiving of email. Any IT guy will tell you that you cannot depend upon users to kept decent (or any) records. IT has to do the achieving centrally.
Keep the heat on. Tell that smarmy new bald headed IRS chief to produce Lois' emails or go to jail for contempt of Congress.