I'm not a proper teacher.
As a tutor, working one-on-one, I obviously work very closely with parents and we always talk at length before I start working with their children.
However, as a parent whose kids are now both in university, we've had both teachers who want to hear from me before classes start, and teachers who prefer I don't bother them.
I well remember one who told me at our first meeting that she hadn't read my son's IEP because she liked to "form her own opinion". I pointed out that if she
had she'd have known he was mildly hard of hearing, as well as quite dysgraphic, and not stuck him at the back of the class or accused him of not trying hard enough when his writing was illegible. She turned out to be quite an okay teacher in the long run, but I thought it really was a rougher start to the year than it needed to be.
I've known others, though, who seemed quite open to talking to me before classes started (or sometimes even as the previous year was winding down), and those were always our favourite teachers. So much hassle can be avoided with just a word or two.
As you can no doubt tell by the responses in this thread, some teachers will very much appreciate your email, and some won't. However, I don't think it can hurt to try, especially if you keep it short and sweet, and frame it as a, "Here's my contact info, we're excited to have you as our teacher this year, and here's a line or two about my child."