Question, Ipod touch and e-mail ?

You know how Ipod touchs (and iphones I'm sure) have the mail 'app' It is one you cannot delete off the ipod & i have my email on it but sometimes when I let friends borrow it they end up reading my emails, and no one wants others to read they're email :P Do you know if I can delete my e-mail from mail or sign out ? I have a feeling the answer is obvious :P *thanks in advance* :)