Storage of your e mail
You may not think about it too often, but, if you work at a large company, most of them have systems that archive all the e mail going in and out, and back it up. Imagine you need a e mail that you got 2 years ago, to prove your high profile case at the top law office, you would count on that e mail being retrievable, and backed up. Email archiving is just that, and there are companies with plans out there who can help you control, and back up your companies e mail for just such a occasion.