While not entirely relevant or applicable to most people today, I was amused at some of the quotes about how, even in 1922, letter-writing was becoming less frequent and that one’s daily mail was more bills and advertising than correspondence.
And even some of Ms. Post’s no-no’s would be welcome in my mailbox (or even my email in-box).
From Emily Post’s Etiquette (1922). You can also read her advice on writing shorter correspondence or any other section from the book.