In 7.5.2 , there is no way to search REGISTRATION_EMAIL

Solution :
in membersearch.php :
Code
if ($email) {
  $email = addslashes($email);
  //$extra .= " and t2.USER_REAL_EMAIL LIKE '%$email%' ";
  $extra .= " and (t2.USER_REAL_EMAIL LIKE '%$email%'  or  t1.USER_REGISTRATION_EMAIL LIKE '%$email%') ";
}

English is not my native language. I try my best to express my thought precisely. I hope you understand what I mean. If any misunderstanding results from culture gaps, I apologize first.