Punctuating a Salutation of a Letter on a Line By Itself

Which is technically correct in terms of punctuation when the salutation of a correspondence is on a line by itself?


Hi, Aspara Gus,


Blah blah blah ...


Thanks.


Bob

_________________________

Hi Aspara Gus,


Blah blah blah ...


Thanks.


Bob

_________________________


Hi, Asparagus—


Blah blah blah ...


Thanks.


Bob