How do you properly address a letter to a woman?

The honorific Ms. is used when you do not know the marital status of the woman or she does not like or use Miss. or Mrs.

Followed by her initials in the case of a formal or business letter or her first name, in the case of a personal friend and then her last name.

ie. Ms. A. S. Brown -formal or business marital statics unknown or Ms. Ann Brown -informal or personal note.

The honorific Miss is used when the woman is unmarried, most commonly in formal or business letters followed by her initials and last name. In formal circumstances Miss is followed by her first and last name.

ie. Miss B. T. Ford -formal or business letter or Miss. Bethany Ford -informal or personal note.

The honorific Mrs. is used when the woman is married or widowed. This is where it gets complicated.

The old-fashioned and formally correct way to address a married woman is by her husband's first and last name.

ie. Mrs. C. E. Jones. -formal and used even if she is a widowed or Mrs. Charles Jones in less formal cases. or Carol Jones - personal notes only

- Please note the use of Mrs. followed by the woman's first name is formally reserved for a divorced woman still using her husband's name.

ie. Mrs. Carol Jones - formal address to a divorced woman.