Whatever you do, do not use "dear". If in doubt, keep it professional (Title Last Name). "Best Regards" is a simple safe catch all closing. The relationship with the person you are messaging is the key. For customers, I always keep it profession and direct, and over time, I will loosen up if I feel they are an easy going person. For vendors, I am more relaxed. After the third response in the chain of email, I stop addressing the person and signatures. The exception is if there are more people attached in the email.
You're doing fine with or without "hi" or "dear." If it's no trouble, just be consistent; keep starting your emails with the same thing. What's the harm? But it's not necessary, as others have said. I like the extra "hi" or "dear" or whatever, but I'm old-fashioned. Basically, as long as you don't treat people on email as if they are a short-order cook (i.e. "where's my reply? I am waiting!" or "I need you to..."), then you will be fine. Bonus points for spell-checking. Polite is how you phrase your question or request and not about how you address someone, at the end of the day. Glad you are asking these questions -- it's crazy some of the email I see from students these days. I had one that started , "I dunt mean to be an ashole..." Jumping Jehovah! That student was new to the country and didn't understand what the word ******* really meant, in tone.
****ing amen to this. A lot of my students end their emails with "I need a response right away." Well, I've got a life lesson headed your way.
