Which one is the most appropriate when I do not know whether I'm writing to a man or to a woman? 'Dear Sirs' or 'Dear Sir or Madam': which one would you recommend?

For example: Dear Ms M Coles. If you don’t know the person/people then use Dear Sir/Madam. Remember, add a comma after their name. 3. Beginning the letter Your opening sentence should get to the ...

A London council has banned all staff from starting letters with ‘Sir’ or ‘Madam.’ The changes are set out in a 17-page document written up by Hackney Council, who believe that calling ...