Depending on your ISP and your e-mail settings, it may still be on your ISP's server. You can normally log into your e-mail on the ISP'S site via a Web browser. It may still be in your in-box or in your trash folder there. This should be so easy to do that I'd try it before trying to get the information another way.

Failing that, most ISPs can retrieve deleted e-mails for 30 or so days back. You'll have to call their tech support, but they can almost certainly do it.