The only advantage to Internet Explorer is the occasional web site that will not function correctly without the presence of ActiveX. Fortunately, the world has slowly, and mostly learned that ActiveX was one of the worst ideas ever invented (not just my opinion). Very few sites exist anymore that use it. A smart move since not every person in the world does, wants to, or even can use IE. An excellent way to lose a possible customer to a competitor by trying to force the use of a single type of browser.
Not that it stops some web masters from running a check to see if IE is the browser being used to access a site, and won't load unless it does; even if it makes no difference what browser you're using to the site's functionality.
Emails are another matter. Generally, it's difficult to pull emails out of one type of email client and bring them into another. It almost always requires some type of conversion utility. Look to see if the store left a .mbox file on the drive somewhere. Logically (at least to me), they may have dropped it in the Documents folder of your user account.