We're in the midst of evaluating Zimbra, and upgraded from 4.5.10 to 5.0 in January.
We're seeing problems with every client having mail that won't sync (i.e. it's visible in webmail or via IMAP, but won't sync into Outlook).
Here's an example timeline:
User has a VM running XP under OSX & last had it running on 12/9/2007
We upgraded from 4.5.10 5.0 on 1/9/2008
Today the user ran the ZCO installer to upgrade to the latest ZCO and then started Outlook.
No mail from between 12/9/2007 and today will sync. Any new mail that comes in shows up right away.
Anyone else seen this?