Thank you Achim !!
As Dirk, I copied the five lines at the botom of both the files :
- /etc/syslog-ng/syslog-ng.conf.in
- /etc/syslog-ng/syslog-ng.conf
And as Dirk, after having restart the syslog-ng, the filesize of /var/log/zimbra.log was not 0 anymore.
I launched the Zimbra services, and check /var/log/zimbra.log : now it works.
But not as Dirk, in my web admin, I haven't the error message anymore. I can see the list of the services running
Thank you very much for your help !