Geraldine Woods says (English Grammar for Dummies):
"When writing a message to someone, you need to separate the person's name form the rest of the sentence with a comma. Otherwise, your reader may misread the intention of the message."
She gives the example:
"Lochness wants to kill Wendy. I locked him in this room," which may have two different interpretations depending on whether you put a comma after 'kill' or not.
PS Not a native speaker
Interested in Language