If you address a woman, married or single, the salutation in business letters is Dear Madam; as,

1

Mrs. John Pierce,
Seattle, Wash.
Dear Madam:

2

Miss Florence Pierce,
Seattle, Wash.
Dear Madam:

A more familiar form of salutation is either of the following:

1

Miss Florence Pierce,
Seattle, Wash.
My dear Miss Pierce:

2

Miss Florence Pierce,
Seattle, Wash.
Dear Miss Pierce: