How To Write A Formal Letter Yours Sincerely . The oxford handbook of commercial correspondence follows fowlers’ reasoning with more specifics. If the recipient is unknown, do not use “yours sincerely.”. Cover letter sincerely or faithfully from sncedirect.web.fc2.com It’s one of the more polite ways we can give someone a command or order if we’re above them. The principle school name date subject:_____ respected ma’am content yours truly name , class, roll no. You should use “yours faithfully” when starting the letter with “dear sir/ madam ” or when you don’t know the recipient’s name.