What's a good way to start an email to some one you've never met?

I’m trying to address an email to a teacher I have never met. “Dear” seems awkward, “To whom it may concern” doesn’t fit and just starting with his name seems informal…

I’m trying to convince the guy to let me into his accounting class. I would have signed up earlier, but I had to wait for my transcripts to transfer schools. Now all the accounting classes are booked and I can only get in if I ask a teacher.
=/ And advice?