diff --git a/lib/kolab_sync.php b/lib/kolab_sync.php
--- a/lib/kolab_sync.php
+++ b/lib/kolab_sync.php
@@ -82,7 +82,7 @@
         //          e.g. are not using output or rcmail objects or
         //          doesn't throw errors when using them
         $plugins = (array)$this->config->get('activesync_plugins', array('kolab_auth'));
-        $plugins = array_unique(array_merge($plugins, array('libkolab')));
+        $plugins = array_unique(array_merge($plugins, array('libcalendaring', 'libkolab')));
 
         // Initialize/load plugins
         $this->plugins = kolab_sync_plugin_api::get_instance();
diff --git a/lib/kolab_sync_data.php b/lib/kolab_sync_data.php
--- a/lib/kolab_sync_data.php
+++ b/lib/kolab_sync_data.php
@@ -92,6 +92,11 @@
     protected $imap_folders = array();
 
     /**
+     * Shortcut to logging.
+     */
+    protected $log;
+
+    /**
      * Timezone
      *
      * @var string
@@ -186,6 +191,8 @@
 
         $this->defaultRootFolder = $this->defaultFolder . '::Syncroton';
 
+        $this->log = Syncroton_Registry::get('loggerBackend');
+
         // set internal timezone of kolab_format to user timezone
         try {
             $this->timezone = rcube::get_instance()->config->get('timezone', 'GMT');
@@ -954,18 +961,16 @@
                     $crc = $matches[1];
                     $uid = $matches[2];
 
-                    if (strlen($entryid) >= 64) {
-                        foreach ($folder->select(array(array('uid', '~*', $uid))) as $object) {
-                            if (($object['uid'] == $uid || strpos($object['uid'], $uid) === 0)
-                                && $crc == $this->objectCRC($object['uid'], $folder)
-                            ) {
-                                $object['_folderid'] = $folderid;
-                                return $object;
-                            }
+                    foreach ($folder->select(array(array('uid', '~*', $uid))) as $object) {
+                        if (($object['uid'] == $uid || strpos($object['uid'], $uid) === 0)
+                            && $crc == $this->objectCRC($object['uid'], $folder)
+                        ) {
+                            $object['_folderid'] = $folderid;
+                            return $object;
                         }
-
-                        continue;
                     }
+
+                    continue;
                 }
 
                 // Or (faster) strict UID matching...
diff --git a/lib/kolab_sync_data_calendar.php b/lib/kolab_sync_data_calendar.php
--- a/lib/kolab_sync_data_calendar.php
+++ b/lib/kolab_sync_data_calendar.php
@@ -506,6 +506,65 @@
      */
     public function setAttendeeStatus(Syncroton_Model_MeetingResponse $request)
     {
+        /*
+         * The request actually involves an iTip request.
+         *
+         * - Get to the iTip,
+         * - Extract the event UID,
+         * - If not already an event in the user's calendar(s), create the event,
+         * - If already an event, update that event.
+         */
+
+        $object = $this->parseMessageId($request->requestId);
+        $message = new rcube_message($object['uid'], $object['foldername']);
+
+        // Parse the message
+        $libcal = libcalendaring::get_instance();
+        $libcal->mail_message_load(array('object' => $message));
+        $ical_objects = $libcal->get_mail_ical_objects();
+
+        $uid = $ical_objects->objects[0]['uid'];
+
+        // Search the user's (event) folders
+        $folders = $this->listFolders();
+
+        $serverIds = Array();
+        foreach ($folders as $folder => $attrs) {
+            $serverIds[] = $this->serverId($uid, $attrs['imap_name']);
+        }
+
+        // Go search for a match
+        $existing_event = NULL;
+
+        foreach ($serverIds as $serverId) {
+            foreach ($folders as $folderid => $attrs) {
+                $existing_event = $this->getObject($folderid, $serverId);
+                if ($existing_event !== NULL) {
+                    break;
+                }
+            }
+
+            if ($existing_event !== NULL) {
+                break;
+            }
+        }
+
+        /*
+            Consider;
+
+            - $existing_event->sensitivity (private, confidential, public)
+            - $existing_event->attendees[$x]->{role,rsvp,status}
+            - $request->userresponse
+        */
+
+        if ($existing_event !== NULL) {
+            // This is an existing event that needs updating
+            $this->log->debug("This is an existing event that needs updating");
+        } else {
+            // This is a new event
+            $this->log->debug("This is a new event");
+        }
+
         // @TODO: not implemented
         throw new Syncroton_Exception_Status_MeetingResponse(Syncroton_Exception_Status_MeetingResponse::MEETING_ERROR);
     }
@@ -698,4 +757,26 @@
             $entry->endTime = $rounded;
         }
     }
+
+    private function parseMessageId($entryid)
+    {
+        // replyEmail/forwardEmail
+        if (is_array($entryid)) {
+            $entryid = $entryid['itemId'];
+        }
+
+        list($folderid, $uid) = explode('::', $entryid);
+        $foldername = $this->backend->folder_id2name($folderid, $this->device->deviceid);
+
+        if ($foldername === null || $foldername === false) {
+            // @TODO exception?
+            return null;
+        }
+
+        return array(
+            'uid'        => $uid,
+            'folderid'   => $folderid,
+            'foldername' => $foldername,
+        );
+    }
 }