If you are writing to someone who has a doctorate or medical degree, use the abbreviated form: "Dr." However, for other titles, such as professor, judge, rabbi, etc., write out the full title and capitalize it. For example, your salutation in a letter to a judge would be, "Dear Judge Barnard." Or, if your correspondence was with a rabbi, you might write, "Dear Rabbi Williams."
Parts of Business Letter. A business letter will be more impressive if proper attention is given to each and every part of the business letter. There are 12 Parts of Business Letter. The Heading or Letterhead,Date, Reference, The Inside Address, Subject, Greeting, Body Paragraphs, Complimentary Close, Signature and Writer’s Identification, Enclosures , Copy Circulation, PostScript