Social Letters
The salutation, or complimentary address to the person to whom the letter is written, in a social letter should begin at the left-hand side of the sheet about half an inch below the heading and an inch from the edge of the paper. The form "My dear" is considered in the United States more formal than "Dear." Thus, when we write to a woman who is simply an acquaintance, we should say "My dear Mrs. Evans." If we are writing to someone more intimate we should say "Dear Mrs. Evans." The opposite is true in England—that is, "My dear Mrs. Evans" would be written to a friend and "Dear Mrs. Evans" to a mere acquaintance. In writing to an absolute stranger, the full name should be written and then immediately under it, slightly to the right, "Dear Madam" or "Dear Sir." For example:
Mrs. John Evans,
Dear Madam:
or
Mr. William Sykes,
Dear Sir:
The salutation is followed by a colon or a comma.
Business Letters
In business letters the forms of salutation in common use are: "Dear Sir," "Gentlemen," "Dear Madam," and "Mesdames." In the still more formal "My dear Sir" and "My dear Madam" note that the second word is not capitalized. A woman, whether married or unmarried, is addressed "Dear Madam." If the writer of the letter is personally acquainted with the person addressed, or if they have had much correspondence, he may use the less formal address, as "My dear Mr. Sykes."