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Where should the comma be placed in the salutation of a letter?
I am not sure if the way I have formulated the title of my question is correct, so if you know better, please, edit it.
The question is simple: Whenever I thank anyone for his or her answer or comments I usually write (eg) "Thank You, George, for Your answer", or "Thank You, Silverglass, for telling me that". Usually in such phrases I place commas on either side of the address, but I don't know if it's correct in English or not.
What about greetings in the very beginning of an e-mail? I do place commas there before the address:
Hi, Mark,
How have you been? It's been...
or
Hello, Peggy!
Do you know of any...
but I have seen many times that commas before the address were omitted ("Hello Mark," or "Hello Peggy!"). So, which way is correct?
