Is it ever appropriate to use Dear Sir or Madam?

While the classic greeting, “Dear Sir or Madam,” is still acceptable, it should be used with caution. Because it is an old standard, it can sound stuffy, and those who don’t conform to binary genders may be offended by this salutation — not the way you want to start off your first interaction with a potential employer.

Is it appropriate to use "Dear Sir or Madam" in a cover letter or email?

A cover letter is more formal than an email, but you should still use “Dear Sir or Madam” sparingly. As with an email, make every effort to be as specific as possible. If you do find that you need to use this greeting, make sure you use the body of your letter to show that you’ve done your research on the company and position.

What is the difference between "Dear Sir" and "Dear Sirs"?

“Dear sirs” is grammatically correct in an email or letter when addressing more than one man. If you do not know for certain that you are only addressing men, you would be better off using a gender-neutral term (like “dear all”). “Dear sirs” only works when addressing men.