I've been using Zimbra desktop for Mac for quite a while to connect to our corporate zimbra account as well as to gmail.
I am pretty happy about it, but there are two major issues that really bother me. One is here, and the other is in my other thread
My inbox does not automatically refresh when new messages arrive.
If I leave ZD open, with focus on the inbox, then the inbox will not refresh unless I move to a different folder and then switch back to it.
This is pretty annoying and has already caused me to miss urgent emails while I was busy and concentrated on other tasks!