Letters

[Unregistered]

Do you say "Madame" or "Madam" in a letter to someone who you don't know if it is male or female? This is because my english teacher taugh me that it was "Madame" and I read in the forum "Madam". I don't know which one is right! I would really apreciate if you could answer me the earliest, because I am gonig to have a test tomorrow.
Thanks for the attention payed.

[Tdol]

I'd use 'Madam'.