If you know the name of the person, start with Dear Mr. Jones, Mrs. Brown or Ms. Smith (if the woman isn’t married) and finish the letter or email with Yours sincerely to show you are open and have nothing to hide! Interesting point: The etymology of ‘sincerely’ is of French origin which means WITHOUT WAX/SENZA CERA because wax was used TO SEAL/SIGILLARE private or secret letters in the past before PEC 😉
If you don’t know the person, use Dear Sir/Madam (not Dear Sirs!)
To finish the letter use Yours faithfully (in fede)!
Happy letter writing!