How should you write "To Whom It May Concern" in a letter?

When writing a formal letter, it is important to capitalize the first letter of each word in the phrase "To Whom It May Concern" and to use "whom" instead of "who" or "whomever". Additionally, it is more appropriate to follow the phrase with a colon and add two spaces before beginning your message. This phrase should only be used when sending something to an unknown recipient.