> It is generally considered polite to address a woman by Ms. rather than Mrs., unless the preference of the woman in question is clearly known. This is especially true in written communication, as dictated by professional etiquette.[1]

> [Ms. is] intended as a default form of address for women regardless of marital status. [2]

[1] https://en.wikipedia.org/wiki/Mrs. [2] https://en.wikipedia.org/wiki/Ms.