Salutation: (Two lines below the recipient’s address, or about 1Ǚ down the page) The person the letter is intended for. Avoid “Dear Sir/Madam” and especially “To Whom it May Concern” unless absolutely necessary; not directing a letter to an exact recipient suggests that you don’t care who reads it (or you would have made a call or checked their website) _ and may prevent the letter from reaching someone who can act on your letter.
Anything that you'd use in an informal communication is inappropriate for a business letter. This includes slang, text_speak, emojis, and anything off_color or casual. If you're used to communicating mostly with friends, family, or even co_workers you've worked with for a long time, an appropriate closing for a business letter will probably feel pretty stilted at first. Don't worry about it – your colleague or business associate won't feel that way when he or she reads your correspondence. What seems unnatural to you will feel respectful and polite to the recipient.