I had a look at a zimbra demo and I am impressed. after reading the docu I found out it is installing its own apache and mailserver (if I remember right postfix) is there a way to make zimbra happy with an existing ispcfg install? the webmail is just too cool
I dont think zimbra will work with ISPConfig, their setup is incompatible and zimbra changes the postfix main.cf with its own admin tools.