I would like to see a howto on Zimbra and ISPconfig, either on the same machine or on 2 machines. I think that the mail abilities of Zimbra make it something we should all examine, and the organization, and billing features make ISPconfig one of my favorite applications. To use these together somehow, I think that tutorial would be of value!
Zimbra needs it's own setup and cannot be shared with other tools like ISPConfig. You can use two servers and configure external mailserver in ISPConfig. That works.
I currently run ISPconfig, but I do not see where to put in the external mail server configuration. Could you perhaps be more specific?
Goto your site (ISP Manager -> Expand -> your_sitename) to get the overview screen of the site with tabs. Click on the tab "Options" and change the drop down box for mail server. About Zimbra: there are of course possibilities to extend ISPConfig with SOAP calls towards Zimbra (can even be done over the network, separate systems) and thus integrate Zimbra and ISPConfig. I have recently done a Proof of Concept of such a setup to integrate Zimbra with a propriety Control Panel.
Like I said, a propriety, custom developed for a specific hosting company in Europe. Not one of the known ones like Plesk or DirectAdmin and such. About integration with ISPConfig: I've been (and still am) working on a contract past 7 months, and have little to no time to work on OpenSource projects or make some contributions here. Much to my regret, but hey, cloning yourself is still not an option in the OpenSource world, is it? Martin