private function _checkForMailSent($isNew, array $context)
    {
        // Never change on new tokens
        if ($isNew) {
            return false;
        }

        // Only act on existing valid from date
        if (! (isset($context['gto_valid_from']) && $context['gto_valid_from'])) {
            return false;
        }

        // There must be data to reset
        $hasSentDate = isset($context['gto_mail_sent_date']) && $context['gto_mail_sent_date'];
        if (! ($hasSentDate || (isset($context['gto_mail_sent_num']) && $context['gto_mail_sent_num']))) {
            return false;
        }

        // When only the sent_num is set, then clear the existing data
        if (! $hasSentDate) {
            return true;
        }

        if ($context['gto_valid_from'] instanceof \Zend_Date) {
            $start = $context['gto_valid_from'];
        } else {
            $start = new \MUtil_Date($context['gto_valid_from'], $this->get('gto_valid_from', 'dateFormat'));
        }

        if ($context['gto_mail_sent_date'] instanceof \Zend_Date) {
            $sent = $context['gto_mail_sent_date'];
        } else {
            $sent = new \MUtil_Date($context['gto_mail_sent_date'], $this->get('gto_mail_sent_date', 'dateFormat'));
        }

        return $start->isLater($sent);
    }