The phrase "nice to greet you" is something that is never used in my experience. You could use "nice to meet you" even though you have never really met the person. You could also use "Greetings" or " It is nice to make your acquaintance". I hope this helps.

I wouldn't use either. I would just open with "Dear Mr/Ms ___", then explain who I am and why I am emailing them. Then close with "Yours truly" or Best regards".

Wal, It depends too on if this is an informal exchange or not! Good luck.

Thanks very much.