Like public relations letters, social business correspondence does not promote immediate business. astute businessperson will recognize the writing of a letter of congratulations or appreciation as a fertile chance to build goodwill. The occasions call for social business letters are many; such letters may express congratulations, sympathy, or thanks, or may convey an in- vitation or announcement. These message may be extended to friend and personal acquaintances, to co-workers and employees, and to busi ness associates. They may even be sent to persons who are unknown to the writer but who represent potential customers.