You are writing a letter to a principal
Formal
You are writing an invitation to your birthday party
Neutral
You are writing an email to make a reservation at a restaurant
Formal
You are writing an application for University
Formal
You are applying for a job
Formal
You are writing a play about a group of school kids
Informal
You are sending a message to an old friend on social media
Neutral
You are communicating to someone you do not know
Formal
You are writing a song
Informal
You are writing an essay
Formal
You are sending a message to a friend
Informal
You are communicating with a potential client
Formal
You are writing an instagram caption
Your choice
You are writing a personal blog
Your decision
You have an assignment to write an informal email
Informal
You are writing to a manager at work
Formal
You are writing an article for a school magazine
Neutral
You are writing a petition
Formal