It's a dedicated Server (not behind a router or anything like that)...
I didn't change anything within the "/etc/apache2/Vhosts_ispconfig.conf" (just uncommented some lines out as reported in the mainthread for testing). The original config-file doesn't work!
When I open a Domain, which points on my serverip, like www.example.com
in my Browser, I am being referred to the "/var/www/sharedip" folder. (Placed a special index.html within sharedip to ensure that.)