I've lost one email address to the ether thus far. My cousin told someone the answer to the 'secret question' (Back when you couldn't make your own, and there were just a few generic choices).
It doesn't matter now, my old address has died a death and nothing of value was lost.
Depending on what you used your old email for, and if you have the computer that you used to use it on (unformatted, with files from that era intact), you could always look through things like your web history and chat logs of your messenger client.
Failing that, if you know of any sites that are still standing that you used that email in the account settings, then log in and find out the address.
If it doesn't work, then I'd assume that you're doomed as the email provider may have pruned your account for 3 years inactivity.