Fresh install - Kopano WebApp PHP mapi extension not found




I have a fresh install of a testing environment - 1 PDC, 1 BDC, 3 Memberserver.
On one Memberserver I successfully installed Kopano Core and the WebApp. When trying to access the WebApp following error occurs:

Not Found: PHP mapi extension not found
If you have upgraded Kopano Core, please restart Apache

I already tried:

UCS 4.3.0-112
Kopano WebApp can’t start because of incompatible configuration.

Please correct above errors, a good start is by checking your '/etc/php5/apache2/php.ini' file.

You can disable this configuration check by editing the file '/usr/share/kopano-webapp/config.php', but this is not recommended.

Apache Log:

[Fri Jun 08 09:08:50.991245 2018] [autoindex:error] [pid 9781] [client] AH01276: Cannot serve directory /var/www/univention/js/umc/: No matching DirectoryIndex (index.html,index.cgi,,index.php,index.xhtml,index.htm) found, and server-generated directory index forbidden by Options directive, referer:



this has been discussed multiple times within the last couple of weeks, e.g. here:

Kind regards