Hallo,
thank everybody that tried to help.
Yesterday the host-server of my vps stopped working. The provider informed me that due to hardwarefailers the hardware has to be changed.
Two hours ago the system was available again. And Zimbra worked!
So the reason for the error seames to be the hardware failure. But the provider denied last week that they were responsible. They offerd only charged support. When I asked for compensation if the reason is caused by the provider they told me that they will not support me. To fix the problem I should reinstall my vps. I did so without eleminating the error.
Regards,
Friedmar