diff --git a/lib/ext/Syncroton/Command/Sync.php b/lib/ext/Syncroton/Command/Sync.php
--- a/lib/ext/Syncroton/Command/Sync.php
+++ b/lib/ext/Syncroton/Command/Sync.php
@@ -651,7 +651,7 @@
                     if(is_array($collectionData->syncState->pendingdata)) {
                         $serverModifications = $collectionData->syncState->pendingdata;
                         if ($this->_logger instanceof Zend_Log) {
-                            $this->_logger->info(__METHOD__ . '::' . __LINE__ . " restored from sync state: (added/changed/deleted) " . count($serverModifications['added']) . '/' . count($serverModifications['changed']) . '/' . count($serverModifications['deleted'])  . ' entries for sync from server to client');
+                            $this->_logger->info(__METHOD__ . '::' . __LINE__ . " restored from sync state: (added/changed/deleted) " . count($serverModifications['added']) . '/' . count($serverModifications['changed']) . '/' . count($serverModifications['deleted']) . ' entries for sync from server to client');
                         }
                     } else {
                         try {
@@ -777,7 +777,7 @@
                 if ($this->_logger instanceof Zend_Log) {
                     $this->_logger->info(__METHOD__ . '::' . __LINE__ . " Processing collection " . $collectionData->collectionId);
                 }
-                
+
                 // send reponse for newly added entries
                 if(!empty($clientModifications['added'])) {
                     foreach($clientModifications['added'] as $entryData) {
diff --git a/lib/kolab_sync_data_email.php b/lib/kolab_sync_data_email.php
--- a/lib/kolab_sync_data_email.php
+++ b/lib/kolab_sync_data_email.php
@@ -393,7 +393,7 @@
             $result['messageClass'] = 'IPM.Note.SMIME.MultipartSigned';
         } elseif ($headers->ctype == 'application/pkcs7-mime' || $headers->ctype == 'application/x-pkcs7-mime') {
             $result['messageClass'] = 'IPM.Note.SMIME';
-        } elseif ($event = $this->get_invitation_event_from_message($message)) {
+        } elseif ($event = $this->get_invitation_event_from_message($message, true)) {
             // Note: Depending on MessageClass a client will display a proper set of buttons
             //       Either Accept/Maybe/Decline (REQUEST), or "Remove from Calendar" (CANCEL) or none (REPLY).
             $result['messageClass'] = 'IPM.Schedule.Meeting.Request';
@@ -1461,26 +1461,38 @@
     /**
      * Returns calendar event data from the iTip invitation attached to a mail message
      */
-    public function get_invitation_event_from_message($message)
+    public function get_invitation_event_from_message($message, $ignoreErrors = false)
     {
-        // Parse the message and find iTip attachments
-        $libcal = libcalendaring::get_instance();
-        $libcal->mail_message_load(['object' => $message]);
-        $ical_objects = $libcal->get_mail_ical_objects();
-
-        // Skip methods we do not support here
-        if (!in_array($ical_objects->method, ['REQUEST', 'CANCEL', 'REPLY'])) {
-            return null;
-        }
+        try {
+            // Parse the message and find iTip attachments
+            $libcal = libcalendaring::get_instance();
+            $libcal->mail_message_load(['object' => $message]);
+            $ical_objects = $libcal->get_mail_ical_objects();
+
+            // Skip methods we do not support here
+            if (!in_array($ical_objects->method, ['REQUEST', 'CANCEL', 'REPLY'])) {
+                return null;
+            }
 
-        // We support only one event in the iTip
-        foreach ($ical_objects as $mime_id => $event) {
-            if ($event['_type'] == 'event') {
-                $event['_method'] = $ical_objects->method;
-                $event['_mime_id'] = $ical_objects->mime_id;
+            // We support only one event in the iTip
+            foreach ($ical_objects as $mime_id => $event) {
+                if ($event['_type'] == 'event') {
+                    $event['_method'] = $ical_objects->method;
+                    $event['_mime_id'] = $ical_objects->mime_id;
 
-                return $event;
+                    return $event;
+                }
+            }
+        } catch (\Exception $e) {
+            // To minimize occurrence of fatal errors while syncing, which would stop the whole process,
+            // we ignore any exceptions on parsing iTips. This allows the email message to be syncrotnized
+            // anyway, without stopping the sync process. We make it optional as there are cases which should throw.
+            if (!$ignoreErrors) {
+                throw $e;
             }
+
+            $id = kolab_sync::get_instance()->get_user_name() . '/' . $message->folder . '/' . $message->uid;
+            rcube::raise_error("Failed to parse iTip message in {$id}. " . $e->getMessage(), true);
         }
 
         return null;