Yes, but you may safely drop the “e” at the end of “Madame.” The rules as of 2010 have changed. According to The Gregg Reference Manual, Tenth Edition, by William A. Sabin, if you don’t know the names of anyone in a large organization, but know there are both men and women, use “Dear Sir or Madam” rather than “To Whom It May Concern,” or “Ladies and Gentlemen” or “Gentleman and Ladies.” Do not use “Gentlemen” alone, unless it is an organization made up of men. You may also omit the salutation. (Section 1340)