Posting this here for reference and perhaps someone will have insight. There were several other threads that mentioned this dll, but none that specifically dealt with the problems we have seen.
Issue: upgrading XP Pro systems with Office 2003 and a working Outlook Connector to Office 2007 would break outlook. Error message referred to a broken MSMAPI32.dll.
After much banging of head against wall it was discovered that the problem actually was an OLD mspst32.dll located in the windows\system32\ directory. Outlook wants to use the one located in it's own office12 directory (generally under "Program Files" somewhere. Outlook either generates a non specific error or the one referring to MSMAPI32.dll when this problem occurs, then dies, which for us has been 100% of the time doing Office upgrades.
The solution is to rename/delete mspst32.dll in the windows\system directory.
Additionally, evidently some Microsoft Updates will put this file BACK, thereby breaking Outlook 2007 again (support nightmare).
This ONLY happens when trying to use the Zimbra Outlook Connector, not when using local pst files or another email source, so has some specific hook to the connector.
It does not appear to matter what version of the Outlook Connector you use, we tried three, from 5.0.x to the latest.
Perhaps it might be usefull for the zimbra connector to do some checking during startup or install to see if this dll is current or as expected?
Vista and Win7 do not appear to have a mspst32.dll in any system directories and do not seem to have any of these problems.