YOURS FAITHFULLY. I posted here about how Debra Tannen’s students treat an e mail to a professor as a formal business document with a “complimentary close”.
I remembered that letters in the Economist used to use “Yours faithfully” as a complimentary close. I checked just now and the Economist is no longer printing “Yours faithfully” at the bottom of each letter—only the letter writer’s name, title, and address. I also did some research. It turns out there is a set of rules on when to use “Yours faithfully” versus “Yours sincerely”. Here is the set of rules on the DifferenceBetween website.
It turns out that: “‘Yours sincerely’ must be used when writing to someone that you have met or spoken to”. On the other hand, “If the person that you are writing to is not an acquaintance then use a more formal tone with a formal salutation and the complimentary close, ‘Yours faithfully.’”
When I was writing business letters regularly, I did not know any of the rules, so for over thirty years I simply used “Very truly yours” on every letter. I still don’t know whether that was correct.