I understand that you followed the installation guide at https://www.bennetrichter.de/en/tutorials/mailcow-dockerized/ to set up Mailcow with self-signed TLS certificates. However, you want to replace the self-signed certificates with Certbot certificates to avoid the browser warnings. When you copied the Certbot certificates to the /opt/mailcow-dockerized/data/assets/ssl directory, the Mailcow instance still seems to be using its original self-signed certificates.