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function is_valid_email($email, $test_mx = false){  
  if(eregi("^([_a-z0-9-]+)(\.[_a-z0-9-]+)*@([a-z0-9-]+)(\.[a-z0-9-]+)*(\.[a-z]{2,4})$", $email))  
    if($test_mx){  
      list($username, $domain) = split("@", $email);  
      return getmxrr($domain, $mxrecords);  
    }else{ 
      return true;
    }
  }else{  
    return false;
  }
}