Madam vs. Ma'am - English Language & Usage Stack Exchange
https://english.stackexchange.com/questions/40905/madam-vs-maam
WebIn formal writing, for example to someone whose name you do not know, use madam in both cases. For example: When addressing a letter to the holder of a particular position without knowing the name or gender of the addressee, it is common to write “Dear Sir or Madam,” (or in the United States, “Dear Sir or Madam:”.
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