E-mailing principals about teaching jobs?

How do I go about e-mailing the principal of a school about being a teacher there. Is it appropriate?? What if I haven't actually seen a posting anywhere about an open vacancy in that building...should I still e-mail? If so, how could I word this e-mail? I'm a recent graduate and really desperate to find a teaching job and would seriously e-mail every principal if I could!! :-P I'm from NY and looking in NC, SC, and GA....North Carolina would be my first choice :)