I will back my statement up based on the fact that I have a bachelor's degree with a minor in English, and that I have a few grey hairs.
We must keep in mind that there is no official sanctioning body that dictates how to use commas in a salutation that includes the word "Hello."
In my years, I have come across many different interpretations on how to technically use a comma. I have also witnessed academics use commas in different ways.
In time, I came to realize that there is an unwritten code when it comes to the rules of writing. I personally describe the code as follows:
First, if you are a college undergraduate, write in the format that your instructor(s) tells you to.
Second, if you are a college graduate, you have earned the right to use your own writing style, unless you are taking a graduate course that has an instructor who requires that you write in a specified style that is different from your preferred style.
Third, college graduates generally respect the writing style of other college graduates whether they agree with the style or not. When reading the written works of a fellow graduate, the objective is to gain an understanding of what the fellow graduate is expressing. If there is a problem with understanding what that person has written that is based on the person's writing style, then the reader respectfully asks (or probes) the writer for clarity and understanding.
The following is an interpretation from The OWL of Purdue University that I feel best indicates how to use a comma:
It states "Use commas wherever necessary to prevent possible confusion or misreading." Reference: https://owl.english.purdue.edu/owl/owlprint/607/
In my opinion, the best thing that a person writing a letter, email, or paper can do, is to account for the reader's ability to comprehend the logic included within their written expression and the reader's ability to read the writing aloud with proper vocal inflections and cadence.
Which one of the following statements make more sense logically or when read aloud?
"I had a peanut, butter, and jelly sandwich for lunch."
Or, "I had a peanut butter and jelly sandwich for lunch."
In the case of the use of the word "Hello" in a salutation, placing a comma after the word "Hello" and then another one after the name neither helps the reader to logically comprehend the point of the comma separating the word "Hello" from the name, nor does it help the reader to read the words aloud with the proper inflections and cadence.
Based on the foregoing, I recommend using the comma after the name when writing a salutation that includes the word "Hello."
Try reading the following two versions aloud:
Hello, Jane,
It was a pleasure spending time with you and the children yesterday.
Hello Jane,
It was a pleasure spending time with you and the children yesterday.
Today, speakers of the English language will generally prefer the latter version (that has only one comma after the word Jane) in written form and when read aloud. Using the other format will make a person sound somewhat robotic when speaking aloud.
Finally, if you are a grade school or college undergrad student, I recommend you ask your instructor which format he or she prefers. Follow that teacher's format and be willing to change formats from teacher to teacher if necessary.
