Is it correct to start a cover letter like this:
"Dear Sir / Madam..." with a forward slash,
or would you rather use
"Dear Sir or Madam..."
when you don't know your recipient's name?
"Dear Sir or Madam," is the standard form. When not addressing someone by name, end with "Yours faithfully," not "Yours sincerely,". However, it is not too difficult to find out the names of people that you are writing to and you should certainly do this if you are making a job application or if you are writing an important business letter.