What is the difference between a noun and a verb?
Nouns are things that are known by their specific name, such as cat, book, or table. Verbs are action words that tell you to do something, such as eat, read, or sit.
Some people say that newsletter is a verb because it tells you to send something to someone. Others say that newsletter is a noun because it is the name of the program that sends out the messages. The correct answer may depend on how you use newsletter in your sentence.
If you use it as the name of a program, then it is a noun. However, if you use it as an action word to describe sending something to someone, then it is a verb.