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..