I also use email with my therapist and it has been very helpful. He said that I am welcome to call or email him, but emailing just seems less invasive to me. I figure he can read (or not) when it is convenient for him and I don't feel like I am intruding and bothering him quite as much. I agree about being clear about ground rules though, it will save a lot of pain and anguish. Initially my T responded to every email with either a call or an email back. After a while he stopped responding and I couldn't figure out what I had done wrong to cause this change. I would agonize every time I sent an email and heard nothing back. It felt like a rejection and like I was bad and had done something wrong. After a couple months of this, I finally got up the courage to ask him about this and basically, if I want a response I need to say in the email that I would like him to answer. He reads them regardless but since many of my emails are just me trying to get things out, there is really no need for him to get back to me about them. Now that I understand how this works for us, I don't have all of that discomfort of waiting and wondering if he will answer or not and why.