Grammar Tips. Comma 9.

Use a comma when a sentence starts with a mild interjection. 

A mild interjection refers to a type of linguistic expression used to convey a speaker's emotions, attitudes, or reactions in a relatively subtle or restrained manner. "Mild" in this context suggests that the interjection is not excessively strong or forceful but rather conveys a moderate or restrained emotional response. Examples of mild interjections include:

• "Hmm"
• "Oh"
• "Well"
• "Ah"
• "Um"
• "Eh"
• "Huh"

INCORRECT: Well thank you for listening to our show.

CORRECT: Well, thank you for listening to our show.

CORRECT: Oh, that’s fabulous.