My experience jibes with inicky46.  You just have to be smart about what you e-mail...if a provider offers an e-mail address, then it's fair to send an e-mail.  But for reasons others mentioned, it's stupid to ask detailed questions in that mail.  Usually, a simple question like "are you available on X day at Y time" will get a response that is either "yes" or "no" and "I need the following information before we continue" or some secondary means of communication ("call my assistant to firm up an appointment").  Some providers PREFER e-mail; others don't use it.  Remember, it works both ways - they don't know who you are, and you don't know who they are, so don't send and don't ask anything detailed.