We are currently testing Zimbra as a replcement for our Cyrus/Postfix combo.
There is a strange issue at one of the computers with Outlook connector plugin.
If a user logs in with a different profile (not the Zimbra one) then after a while his imap mailbox dissappears (usually takes a few minutes).
This is a Vista 32bit with Office 2007 installation.\
We haven't tried to setup his account within his Zimbra profile though to verify if that would work.
This doesn't happen with Windows XP with Office 2007 on other machines which we also are testing the connector on.
If Zimbra sharing plugin is disabled then the issue doesn't happen anymore.