Is mam a proper salutation

"Mam" is not a Word in English. The Word you are thinking of is "Ma'am," which is short for "Madam." In the U.S. we use "Ma'am" primarily in speech. When you are talking to a lady, it is polite to use "Ma'am," especially in the South of the U.S.

In writing a letter, "Madam" is formal and polite. If you are writing to a woman who is in an official position (e.g., a government official), you could start a letter with "Dear Madam." If you are writing to someone in a professional position and you are not sure if it is a man or a woman, you can say "Dear Sir or Madam." If you are addressing a group of people, the salutation is:

Ladies:

Gentlemen:

Ladies and/or Gentlemen:

(The Word "Dear" is dropped.)