Sebastian Dix

“Regards,” “Best wishes,” “All the best” are more personal than the others and less formal, but not appropriate if you don’t know your reader. And there isn’t anything wrong with simply”
― Kenneth Roman, Writing That Works: How to Communicate Effectively in Business

“Thy”
― Augustine of Hippo, Confessions

“What comes after “Dear” is worth some thought. Use first names only when you’re already on a first-name basis. Don’t become anybody’s pen pal by unilateral action. Use titles — Dr., Judge, Professor, Senator — when they apply.”
― Kenneth Roman, Writing That Works: How to Communicate Effectively in Business