“Hi, John” vs “Hi John” – Commas in Salutations

“You use a comma after hi in a salutation, but not after dear.” Click here to find out why.

This is a small thing, but most people seem to get it wrong. Grammar matters, especially in business writing.

In many lines of work, the first and sometimes the only impression customers and other important people have of us is through our writing. Writing thoughtfully, concisely and with proper spelling and grammar shows respect for others’ time and effort.

Taking the time and effort to write well demonstrates that we have high personal standards and are worth considering as a business partner.

Source: http://www.quickanddirtytips.com/education/grammar/dear-comma