In the specific case of the opening salutation I would not insert a comma between the greeting and the name if a comma came after the name, but I would if some other punctuation followed the name.

The following examples all "look correct" to me:

 >   "Hi Mark, how are you?"  
    "Hi, Mark.  How are you?"  
    "Hello Mark, what's up?"  
    "Hello, Mark!  What's up?"

But the "Hi, Mark, how have you been?" example that you gave looks over-punctuated to me.