If doubtful whether to end with "yours faithfully," or "yours truly," or "yours most truly," &c. (there are at least a dozen varieties, before you reach "yours affectionately"), refer to your correspondent's last letter, and make your winding-up at least as friendly as his: in fact, even if a shade more friendly, it will do no harm!
Lewis CarrollOne! two! and through and through The vorpal blade went snickersnack! He left it dead, and with its head He went galumphing back.
Lewis Carroll