I had to email a tutor of mine today and it struck me that i really have no idea what the 'correct' form for a (relatively) impersonal email is supposed to be. Are you supposed to write them like letters:

"Dear Dr. X, blah blah...."

If you just write "Hi, i'm blah blah and i was wondering blah blah blah....." is that considered rude (or maybe blasé, haha)?

Is there a correct email etiquette, or is email too new for social conventions to have set in yet?