[silentium]

This way doesn't work. Data is neve valid. Always that is NOT valid.

$this->form_validation->set_rules($email , 'Users email', 'required|valid_email');

if ($this->form_validation->run() == FALSE)
{
  echo " Submitted data IS NOT valid";
}
else
{
   echo " Submitted data IS valid";
}

$email is the variable where I put the valid email to test. Am I doing something wrong?

Yes, you are.
The form validation do not take variables like that. The first value, where you have $email, is the name of the POST data in global $_POST array. As in my example, lets say that in the AJAX request you do, you send a parameter called 'user_email'. In the controller you send the request to, that 'user_email' data will be available in the global $_POST array as $_POST['user_email']

So, in $this->form_validation->set_rules(); you set the first option to 'user_email' as that is the name of the your data in the global $_POST array.

If you for some reason don't have the data available in the global $_POST array anymore, then you can validate any other type of array. So, in your case, you could create a new array with your email and then set that as the array that form validation should validate.

Here is an example.

PHP Code:

$validate_data = array('email' => $email);

$this->form_validation->set_data($validate_data);
$this->form_validation->set_rules('email' , 'Users email', 'required|valid_email');
 
 if ($this->form_validation->run() == FALSE)
 {
   echo " Submitted data IS NOT valid";
 }
 else
 {
    echo " Submitted data IS valid";
 } 


More info about validation an array here http://www.codeigniter.com/userguide3/li...-than-post