Business emails are usually less formal than business letters because they should be short and to the point. Salutations do not have to be as formal--a simple "hello" is an appropriate introduction to a business email. It is important to remember when writing a business emails is that it can be informal but it should still provide professionalism. Do not reply with single line or words (thank you, etc). Lastly, you do not have to provide the recipient address as you do in a business letter since the receiver can simply reply to the email.
The following is an example of a properly formatted business email:
Suzanne from accounts payable said you would be the one to talk to about our outstanding database fees. Please see the attached bill for further details and get back to me as soon as possible.