Here is why all of Lois Learner's email in the 1st half of 2011 should be available...

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.

The IRS claims they only have 6 months of email back up at anytime. 

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. 

Here is the IRS story about what happened to Lerner's email:

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.

  Email exchange about Lerner hard drive

Here is where the explanation falls apart for losing the 1st six months of Lerner's email. At the time of the Lerner hard drive crash in what appears to be early July of 2011, her email files for the 1st six months of 2011 would be backed up on data tape by the IRS own admission. There may have been other files on Lerner's computer that weren't backed up and were unrecoverable. Actually, since they didn't reuse the tapes for six months, the oldest back up tape likely had several months of email from the end of 2010 too. If Lerner asked them to restore those files, they should be on her new computer. If she didn't ask to have copies of them sent to her, why not? Didn't she want her email anymore? I would think those would be the files someone would most want back. If the IRS can't produce them, they are lying or Lenner didn't want her email back. I will leave the speculation as too why that might be to the reader.