In general,the higher the message goes in the organization,the more formal the tone.

The tone of your business messages can range from informal to conversational to formal. If you're in a large organization and you're communicating with your superiors or with customers, the right tone will usually be more formal and respectful. However, that same tone might sound distant and cold in a small organization or if used with close colleagues. Part of the challenge of communicating on the job is to read each situation and figure out the appropriate tone to use.