Hey: 64 percent Hello: 63.6 percent Hi: 62.7 percent Greetings: 57.2 percent Dear: 56.5 percent All emails: 47.5 percent While you might think that a five to eight point swing in response rate ...

Is "Dear" overly formal? Is "Morning!" too cheery? If you're thinking the email greeting isn't all that important and that it's silly to overthink it, you're wrong.