World-famous photographer Ansel Adams was a great letter writer. We can take a lesson from him. Business letters can be warm and friendly as long as they're not too personal. You have to sense the character of your audience and write accordingly.
Some readers can stand more warmth than others.
In general, it's better to be too warm than too distant. This year Howard Edson wrote his own Christmas card, a small booklet of his thoughts on life. It was the perfect touch. All best wishes, Best wishes for your future, With confidence, Just to keep in touch with you, More shortly, Warmest greetings to all, or Yours always. Remember, the ending of a letter is just as important as the beginning and the middle.