code: public static function mailListTagger(array $list)
      {
          $str = '';
          foreach ($list as $name=>$mail) {
              if (is_string($mail)) {
                  $str .= self::mailTagger($mail, $name).Mailer::$ADDERSSES_SEPARATOR;
              } elseif (is_array($mail)) {
                  foreach ($mail as $subname=>$submail) {
                      $str .= self::mailTagger($submail, $subname).Mailer::$ADDERSSES_SEPARATOR;
                  }
              }
          }
          return $str;
      }
docs: Build a list of person strings compliant to RFC2822
  
  @param string|array $list
  @return string