Zend_Mail::getMessageId PHP Method

    public function getMessageId()
    {
        return $this->_messageId;
    }

 /**
  * set headers in mail to be sent
  * 
  * @param Tinebase_Mail $_mail
  * @param Felamimail_Model_Account $_account
  * @param Felamimail_Model_Message $_message
  */
 protected function _setMailHeaders(Zend_Mail $_mail, Felamimail_Model_Account $_account, Felamimail_Model_Message $_message = NULL)
 {
     if (Tinebase_Core::isLogLevel(Zend_Log::DEBUG)) {
         Tinebase_Core::getLogger()->debug(__METHOD__ . '::' . __LINE__ . ' Setting mail headers');
     }
     // add user agent
     $_mail->addHeader('User-Agent', 'Tine 2.0 Email Client (version ' . TINE20_CODENAME . ' - ' . TINE20_PACKAGESTRING . ')');
     // set organization
     if (isset($_account->organization) && !empty($_account->organization)) {
         $_mail->addHeader('Organization', $_account->organization);
     }
     // set message-id (we could use Zend_Mail::createMessageId() here)
     if ($_mail->getMessageId() === NULL) {
         $domainPart = substr($_account->email, strpos($_account->email, '@'));
         $uid = Tinebase_Record_Abstract::generateUID();
         $_mail->setMessageId('<' . $uid . $domainPart . '>');
     }
     if ($_message !== NULL) {
         if ($_message->flags && $_message->flags == Zend_Mail_Storage::FLAG_ANSWERED && $_message->original_id instanceof Felamimail_Model_Message) {
             $this->_addReplyHeaders($_message);
         }
         // set the header request response
         if ($_message->reading_conf) {
             $_mail->addHeader('Disposition-Notification-To', $_message->from_email);
         }
         // add other headers
         if (!empty($_message->headers) && is_array($_message->headers)) {
             if (Tinebase_Core::isLogLevel(Zend_Log::DEBUG)) {
                 Tinebase_Core::getLogger()->debug(__METHOD__ . '::' . __LINE__ . ' Adding custom headers: ' . print_r($_message->headers, TRUE));
             }
             foreach ($_message->headers as $key => $value) {
                 $value = $this->_trimHeader($key, $value);
                 $_mail->addHeader($key, $value);
             }
         }
     }
 }