4 Dear Sir or Madam is the customary ordering, which is reason enough to do it in a formal setting. But also consider the "rhythm" of the opening; sir has half the syllables as madam, and therefore it sounds better when sir is uttered first. Same thing with Ladies and Gentlemen, where ladies has less syllables than gentlemen.
73 When is it appropriate to use the terms Dear Sir or Madam and To whom it may concern? The rules I was taught state that Dear Sir or Madam should be used when you're writing a letter to a person about something that person has direct involvement in (e.g. returning a defective product to a customer service department).
Is it correct to start a covering letter like this: Dear Madam / Sir, or would you rather use Dear Sirs, or Dear Sir / Madam, Thanks A.
If I were writing a letter of application to a job I would write " Dear Sir / Madam ". I would write " to whom it may concern " if I were writing a pamphlet or circular to the effect that "next week the high street will be inaccessible because electricity cables are being laid". Both are fairly impersonal but the latter implies that the interests of the addressee have very little interest to ...
If the letter begins with Dear Sir, Dear Sirs, Dear Madam, or Dear Sir/Madam, the COMPLIMENTARY CLOSE should be " Yours faithfully ". If the letter begins with a personal name, e.g. Dear Mr James, Dear Mrs Robinson, or Dear Ms Jasmin, it should be " Yours sincerely ". A letter to someone you know well may close with the more informal "Best wishes".