Hi ahmaddanial,
thanks for your support! Further analysis following your remarks showed up, that it seems to be a ldap-server problem. Mattermost can connect on one port, but not search, while from another server (I couldn’t use ldap-check, because no ldapsearch is available in the docker container) I cannot connect on the port mattermost can connect, but can connect and search on the port mattermost fails.
I close here.
BR, Christian