@tgm Yes, but it is not satisfactory. My customers could not really reproduce the problem and they did not report such an issue any more; maybe they are angry about me, Kopano and everything else…
Since last weekend, we use WebApp 5.0.0; it looks really good, the Kopano team did a really good job!
In the past, we had some other problems with inline attachments, so we switched this value to false in /etc/kopano/webapp/config.php:
// Use DOMPurify to filter HTML
// Caution: disabling DOMPurify is a potential security risk.
define(“ENABLE_DOMPURIFY_FILTER”, true);