While I appreciate the elegance of your solution from an engineering perspective the user who accidentally enters an invalid address is definitely getting a worse user experience here. If you're using javascript to validate the email a user will know they've made a mistake immediately. In your scenario they'll see a page telling them that they should receive an email, and then what? They have to start again? If they're lucky they'll think of hitting the back button and full it in correctly. More likely, they'll just think; hmm this email's taking a while to come through, I'll check Facebook... With a bit of luck they'll remember they were trying to sign up for your service, otherwise, you just lost a signup.