I rarely use "good morning" or "good afternoon" in e-mail. Just because I'm writing it then doesn't mean it will be read then (and if I'm writing it to a colleague in India, it's already evening!).
I tend to do this:
However, if I did want to use a "good morning" salutation, I would not bother with the comma before the person's name in e-mail.
Note that I'm in the US and customs here are almost certainly different than they are in other parts of the world.
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