The basic rule is that if you can drop the name and the sentence still makes sense, use a comma. It still applies to greetings, since a greeting is still a greeting whether or not you use a person’s name while doing so.
You wouldn’t use a comma if you said something like “Jack went to work.”
![When you walk into /c/lemmyshitpost to introduce a daily meme series of every line of dialogue from The Room (2003) [Day 1]](https://lemmy.world/pictrs/image/4ebdc47b-0f26-4322-9446-8755b1dd6b9a.png){kind=link}
The basic rule is that if you can drop the name and the sentence still makes sense, use a comma. It still applies to greetings, since a greeting is still a greeting whether or not you use a person’s name while doing so.
You wouldn’t use a comma if you said something like “Jack went to work.”