1. The e-mails are backed up for 6 months. This is actually very normal. Many large companies do this or do it for less time but run on a very similar system (though small ones keep them longer, of course).
2. The reason the IRS doesn't is because it's underfunded and cannot afford it. You can thank the GOP in congress for not increasing its budget enough (in fact, they're slashing its budget!).
3. Most of the e-mails "lost" were found from the correspondents with Lerner. 24k of them, in fact. Not all.
This is another faux-scandal. if there is a real scandal, it's that the IRS isn't funded enough so they can keep more than 6 months (they've actually increased it now, shifting funding from elsewhere) worth and employees can have more than 500MB storage inboxes.
They also tried to save her HD when it crashed but the tech team failed. Not now, back in 2011.
It's pretty hilarious that the GOP thinks an IRS employee sending e-mails all over would crash her own computer (lol) to cover-up something that wasn't discovered and then proven farcical 2 years later.