Steve Leveen in the Huffington Post:
Lewis Carroll didn't live to see the 20th century, let alone the advent of email, but he knew a few things about correspondence. In the course of his career he wrote and received 98,721 letters (we know the precise count thanks to a special letter register he devised to keep track of them).
Lewis Carroll's real name was Charles Lutwidge Dodgson, and he was a professor of mathematics at Oxford. Being a teacher, Dodgson decided to document his advice about how to write more satisfying letters. He did this in a delightful little missive called “Eight or Nine Wise Words About Letter-Writing.”
Although Dodgson knew only handwritten correspondence, I invite you to observe how seven of his suggestions, now 150 years old, might help you with your keyboard correspondence. (His words come first, followed by my commentary, adjusted for email.)
1. “Your friend is much more likely to enjoy your wit, after his own anxiety for information has been satisfied.“
Don't compose your response until you have reread your friend's email, keeping it freshly in mind. Then address your friend's concerns and questions first — even if there is more than one. This way your friend won't have to email you again, asking if you saw what s/he had previously written.