It bothered me when my T didn’t respond. She said that email isn’t useful for therapy and she’d rather we discuss in person. I agree, and said I needed an acknowledgement of email receipt - that’s it. That alleviates a lot of tension I have. She agreed, and since then almost always writes an extra sentence or two. For me not responding is just plain rude; which I expressed to her too, and she’s done her best to reply.