These days many of us use email as a primary source of communication for our businesses.
Emails do seem to lend themselves to a slightly less formal approach than the old fashioned business letter, but how you address your recipient in your email should be appropriate to the level of formality in your relationship.
For instance, unless I know the person really well I never use the word "dear" in the salutation - that just seems too personal to me. That's just me though - use your own judgement.
I also feel that if you know the name of the person you are emailing, you should address them by name. This adds a level of personalization and it also feels more respectful (you know who you are addressing - it's not just some random person).
I usually try to opt for something simple such as "Hi John" or "Good Morning John". Use whatever feels comfortable to you for the situation.
Two things I would definitely recommend:
- Definitely use some sort of salutation especially if it's a first email or the first reply to an email you received (long threads of quick reponses going back and forth can omit the salutation for expediency's sake)
- Spell the recipient's name correctly. To do otherwise is disrepectful. Also, don't shorten the recipient's name to a nickname unless they have done so first. (If they give you their nickname, feel free to use it.)
Remember how you address people is a sign of respect.