In a business letter =P
A salutation ends with a colon when it is used in a formal or business letter or email. It is commonly used before the body of the message, such as "Dear Mr. Smith:".
a colon
A colon should be used after the salutation in a letter using the standard-block style.
salutation
salutation
The situation that requires the use of a colon is d) the salutation of a business letter. In formal business correspondence, it is customary to follow the salutation (e.g., "Dear Mr. Smith:") with a colon to denote the start of the letter's body. In contrast, personal letters typically use a comma after the salutation.
A business letter's salutation should be followed by a colon. For example, "Dear Mr. Smith:" or "To Whom It May Concern:".
Note
Following the name of the recipient in the salutation
Following the name of the recipient in the salutation
A mixed punctuation style typically uses a colon after the salutation.
A comma is not required in the salutation of an editorial letter. You can use either a comma or a colon after the recipient's name. For example, "Dear Editor," or "Dear Editor:".