protected function askEmail()
    {
        $email = $this->ask('E-mail');

        if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
            $this->error("'$email' is not an email address.");
            exit(2);
        } elseif (UserProxy::where('email', $email)->first()) {
            $this->error("User '$email' already exists");
            exit(3);
        }

        return $email;
    }