<?xml version="1.0"?>
<config>
  <modules>
    <Wli_Registrationdemo>
      <active>true</active>
     <codePool>local</codePool>
    </Wli_Registrationdemo>
  </modules>
</config>

<config>
  <modules>
    <Wli_Registrationdemo>
      <version>0.1.0</version>
    </Wli_Registrationdemo>
  </modules>
  <global>
  <events>
    <customer_register_success>
      <observers>
        <Wli_Registrationdemo_customer_register_success>
          <type>singleton</type>
          <class>Wli_Registrationdemo_Model_Observer</class>
          <method>customerRegisterSuccess</method>
        </Wli_Registrationdemo_customer_register_success>
     </observers>
    </customer_register_success>
  </events>
  </global>
</config>

<?php
class Wli_Registrationdemo_Model_Observer {
    public function customerRegisterSuccess(Varien_Event_Observer $observer) {
        $event = $observer->getEvent();
        $customer = $event->getCustomer();
        $email = $customer->getEmail();
        if($email) {
            //Create custom code over here as per your requirements !
        }
    }
}
?>