Here's an example of a perfectly fine informal e-mail to a co-worker:
I'll have those reports ready for you at noon.
But for anything more formal than a casual intraoffice e-mail (that is, for any other situation, including correspondence with an author), use the comma of direct address. See this example of extremely poor taste when the comma is not used:
In our books, I've seen such constructions as these:
Thanks Mrs. Adams.
Fine Bob. Do what you want.
The comma before the person's name or title clarifies the statements: The guys are not hey, no one's commanding anyone to ungrammatically thank Mrs. Adams, we're not expressing that Nancy is OK, and we're not using caveman speech to describe how great Bob is. Or commanding someone to give Bob a fine. Here are the correct ways to punctuate those statements:
Thanks, Mrs. Adams.
Fine, Bob. Do what you want.
Also, a similar rule applies to the use of "oh":
Oh, no, you don't.
Oh, come on . . .
Finally, consider this exchange:
Want some coffee?
It should be No, thanks, meaning No, but thank you for offering. The phrase No thanks is actually saying I'm not thanking you.
Remember these rules when you see dialogue or common expressions in our books. It also doesn't hurt to set a good example by applying these rules in your informal correspondence.