While a simple "Hi," "Hello," or even "Hey" is appropriate in casual correspondence, a more formal salutation is appropriate when you are emailing about a business_related matter, such as a cover letter, letter of recommendation, or inquiry letter.
Business Letter Format: Review a formatted business letter with information on what to include in each section of your letter. When you are writing a business letter, it's important to include an appropriate salutation at the beginning. This is true whether you send your message via email or through the mail. Using an appropriate greeting sets the tone for your letter and shows the recipient that you understand basic rules of business etiquette.