I don't email my T for anything but scheduling issues. I don't know if T allows it, I haven't asked. For me it's important to work on face to face communication.

There are some people here who email their Ts regularly and find it helpful. There are others who run into problems when they email. It seems like the important thing is to talk to your T about what is appropriate out-of-session contact, how much is okay and what kind of reply to expect.