In Chapter 8, I introduced the sign-up feature. But how do you know whether the user has entered a valid e-mail? You need to do some verification to make sure the e-mail address the user entered is a valid e-mail address format. But you don’t really do anything to make sure the e-mail address actually belongs to the user. In the world of e-commerce, e-mail marketing proves to still be effective. So you need a way to verify the e-mail while a user is signing up.