Nuances of punctuation in greetings

The greeting of an email or letter doesn't seem all that important. It's just a little thing next to the actual content of the message, but how one begins has a significant impact on how one ends and what result one gets.

In business writing, the standard greeting to an unknown person is

Dear Mr. White or Dear Ms. White 

depending on the person's gender, obviously.

If the gender is unknown, then you may use the full name without a title, as in

Dear Alex White

However, some people find "dear" too familiar. By "some people" I mean my students, who perhaps are not accustomed to the standard business language that has desensitized all of us from thinking at our bank things we are sweet or that our amazon notifications think we have a close, personal relationship. "Dear" doesn't really mean dear in that way at the beginning of a message.

But, for people dead set against the standard, "Good morning/afternoon/evening" may sound better. I don't particularly like this one because I am not reading the message whenever you send it, so 66% of the time, you're wrong.

Either of these greetings work, even a "Hi" or "Hello" can be appropriate in some circumstances. But if you are using "Good afternoon" or "Hello" you are using a greeting word, so there must be a comma between the greeting word or phrase and the person's name:

Good afternoon, Ms. White

Hello, Mr. White

AND greetings signal the opening of a message with either a comma or a colon after the greeting. For example

Dear Alex White:

Dear Mr. White,

Good afternoon, Ms. White,

Good afternoon, Alex White:

The comma is more familiar, gentler, while the colon is more formal, distancing. Both choices are correct, and you may use them in any circumstances. Generally, I use commas after all greetings. I have only used colons after a few very angry emails that were seeking remuneration, but others may find them more useful on a regular basis.