Can you not just take the Zimbra DnD files from the Zimbra Desktop Prism folder and put them in your own Prism folder?
I use a similar method on the LAN here for our users, except I just used all the Prism stuff from the Zimbra Desktop package, disabled the auto-update feature and pointed it to our Zimbra server.
Another thing you should be aware of is, to my knowledge, that the DnD extension does not currently work with ZCS 6+. |