It really doesn't matter a bit! I started all my e-mails to teachers with "Hi" and that's how I start them to the professors at my uni now. Both my parents and my sister are teachers and they really wouldn't care how the e-mail started!
Whenever I email a teacher it usually depends on the type of teacher it is. If it is a laid back ones I just type the sentence (no Hi/Dear Mrs...). If it's one of those crazy ones that insists everything is super formal then I type dear Mr...
Dear [Their name]
If you call them by their first name usually call then use their first name and last name. If you call them Mrs/Mr usually then use that.
You could possibly get away with saying 'Dear [First name]' only, but I tend to leave that to a reply email.
If I had to send a letter to a teacher (which i do quite a lot as i don't have the guts to ask them face to face for help lol) i always say "Hi Sir" or "Hi Miss"...just try to keep it short because they seriously don't care how it starts...
I'm always emailing my tutors about something or other, but we call them by their first names so we lack the formality in emails... My tutor once used the phrase 'some IT tw*t has deleted the file' which made me giggle.
Thanks a lot,
then when you're replying just miss the 'dear' section as if carrying on a conversation.
Depends on the teacher, what do you call them in lesson?
At my college were dead informal with most teachers, so if i was to email my tutor it would be on a first name basis.
But if you call them miss "so an so" or sir in lesson, then use a more formal style.
I always just write "Hi" or "Hey" but it can depend on what your emailing them about as to how you want to start it. If your in college i assume you know the teacher pretty well so i don't think they would mind it being a bit informal.
Whenever teachers email me they always start it with 'Hi', so I imagine starting it with that or similar variants would be fine. However, I suppose it depends on the teacher, too - if they're pretty uptight then I'd maybe be more formal.