== As an administrator, what do I have to do? ==

If your're terminating SSL traffic at load balancer level, open the server.properties ( /opt/openexchange/etc/groupware/server.properties ) and set


you may find the old option

com.openexchange.cookie.forceHTTPS already configured, in that case just rename it to com.openexchange.forceHTTPS, thereby all links generated by the backend will suggest https is used.