Just a thing- my old t kept email records- printed each email out and filed them. I would explore the possibility of obtaining a hard copy.

I don't think that if anyone picks up the email domain, that they would have access to the previous users emails. once the email is gone, everything would be erased.

I do want to say something- email is not a secure method of communication and that is the reason most therapists discourage email as a means of communicating with their clients. I used to email my old t and then she was accused of being unethical and I lost that relationship. I would be very careful and set good boundaries with whatever t you might have next. (just a story of personal experience)