you can simply add a second email address
the problem is that Freeserve uses a different system (a better system pre-spam days) to most ISPs - so all mail with the address ending:-
will go to your address
if you do not have an email account with freeserve (or orange as they are now) that you pay for each month - you can simply set up a brand new account and use that email address. then just pick up any proper emails from your old account and reply using your new freeserve email address.