Received this feedback from a Zimbra customer today using Windows having moved from Outlook.

Remember however that I do NOT like the Zimbra client because of its lack of integration with the Windows desktop. This problem surfaced again recently in a new guise - we cannot click on an "click here to email me" link on a web page. Even the Zimbra desktop client does not integrate, which I find remarkable. Until Zimbra can fix this, it will never be a real competitor for Outloook, or Thunderbird, or several others, which is a real shame because it has a lot to offer.

As for its server, I have no problems with that whatsoever and it appears to be a very good product..
We are now testing this method, Default Mail Applications (mailto reprised) » Zimbra :: Blog

Any other suggestions? What do you use to integrate Zimbra and mailto links etc. on Windows.