My unsolicited French Lesson of the Day.

M. = Monsieur : Sir / plural: MM. = Messieurs
Mme = Madame : Madam / plural: Mmes = Mesdames
Mlle = Mademoiselle : Miss / plural: Mlles = Mesdemoiselles
In French when you don't know whether the woman you are writing or talking to is married or not, you are supposed to call her Madame (guess this dates back to the times when a woman who was not married was considered a laissée pour compte, i.e. it was an insult just to think that maybe she was not married...). In English it is the opposite, you are supposed to say "Miss" when you don't know her marital status.