I got mine working... These are the steps I use to make it work:
Originally Posted by Saturdays
As an Admin, I went to the registry and make the following changes:
HKEY_CLASSES_ROOT>mailto>shell>open>command and set default as
Next, go to HKEY_LOCAL_MACHINE>Clients>Mail and set the default as
"C:\Program Files\Zimbra\Zimbra Desktop\win32\prism\zdclient.exe" -url "%1"
Exit your registry and restart your computer... You should be all set after you go to internet options>programs> and set Zimbra Desktop as default instead of Outlook.
Let me know if it works for you