$taxoarr is undefined

Set this not assigned to yourself otherwise no one will start looking into the issue.

It is assigned and get to be the value of the object fetching action. The relevant code of the current 6.x -dev version is below as a reference to take a look how it is done:

...
else {
    $result = db_query("SELECT t.tid FROM {term_node} t WHERE t.nid = %d", $edit["nid"]);
    while ($taxoarr = db_fetch_object($result)) {
      // Now for the mailbox.
      switch ($GLOBALS['db_type']) {
      case 'mysql':
      case 'mysqli':
        $result2 = db_query("SELECT * FROM {mailhandler} m WHERE m.commands REGEXP '%s'", 'tid:[[:blank:]]*'. $taxoarr->tid .'[[:>:]]');
        break;
      case 'pgsql':
        $result2 = db_query("SELECT * FROM {mailhandler} m WHERE m.commands ~ '%s'", 'tid:[[:blank:]]*'. $taxoarr->tid .'[[:>:]]');
      }
      while ($mbox = db_fetch_object($result2)) {
        $mboxen[] = array($mbox->mid, $mbox->mailto, $taxoarr->tid);
      }
    }
  }