Facebook sends a notification to every email address associated with an account when someone has been able to register one of the addresses on the account. This happens when a person clicks on a link sent to the email address when creating a new account, or when adding the address to an existing account.
If you still own the email address in question, you can add it back to your account by going to the "Settings" tab on the Account page and following the same process. You may want to change the password for the email address, as someone else may have been able to access it in order to confirm the contact change.
If you no longer own the address, you will not be able to add it back to your account. If you still own the email address but are unable to access it, please contact your email provider for assistance with regaining access to the address.