Comma usage when referring to someone

[SkiIucK]

Hello,
I know commas are always put before addressing to someone, e.g., 'I am very pleased to hear that, dad.' But I don't quite understand why you, people, never put comma in the inaugural part of your posts, i.e., 'Hello Dimitar', 'Hi Alan'. I know my question may sound a bit odd, but I am curious.
Regards

[Torsten]

Hi Dimitar,

I usually put a comma after the opening line as in this message.
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