What determines a good email? Let’s face it, we decide whether or not to open an email the same way we decide whether or not to open a book, by the cover. And that’s why the key to great email starts with the subject line. After the sender name, subject lines are your first point of contact with a customer. It’s where your company can offer value, pique interest, and invite engagement. So, what makes a good subject line? That’s the question our friends at 8tracks.com tackled earlier this year.