Um.. I know that some forums disallow certain email sites from being used, and messages to them won't be delivered. It could also be that Yahoo mail is automatically blocking emails from PC. If you know how to access Yahoo Mail's safe senders list, then I'd try adding PC to it, if I were you. If that makes sense.. xD; I haven't had a Yahoo email in years, so I can't be certain that it has a 'safe list', but it should. Most emails do.