You just need to remove second arguments from rule-- Like you defined as
'rule' => array('email', true)
This should be as-
'rule' => array('email')
after edit on question
You can do this by dynamic validation. But the easy approach will be unset email validation thus you are on development environment..
AppModel.php
public function beforeValidate(){
if$this->validate['email'](){
unset($this->validate['email']);
}
// now, If you really need to check email add dynamic rule for email field here.
}