code: public static function deduplicate($array)
      {
          if (empty($array)) {
              return $array;
          }
          $known = array();
          foreach ($array as $_index=>$entry) {
              if (is_array($entry)) {
                  foreach ($entry as $i=>$_email) {
                      if (!in_array($_email, $known)) {
                          $known[] = $_email;
                      } else {
                          unset($array[$_index]);
                      }
                  }
              } elseif (is_string($entry)) {
                  if (!in_array($entry, $known)) {
                      $known[] = $entry;
                  } else {
                      unset($array[$_index]);
                  }
              }
          }
          return $array;
      }
docs: De-duplicate a set of name=>email pairs to let each email just once
  
  @param array $array
  @return array