"Sir, yours truly."
Letters to persons whom you meet frequently in society, without having
arrived at intimacy, may commence with "Dear Sir," and end with "I am,
dear Sir, yours very truly."
Letters commencing "My dear Sir," addressed to persons whom you
appreciate, and with whom you are on friendly terms, may end with "I
am, my dear Sir, yours very faithfully," or "yours very sincerely."
To be prompt in replying to a letter is to be polite.
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