If you are seeing the following behaviour in Entourage 2008:
* Inbox does not update, but you do see new emails via OWA
* Sent email is sent without issue
* Other user folders on the server update successfully
* Status displays no error messages, simply "Updating inbox..." without any new emails arriving
To resolve this issue we need to empty the cache on the Inbox folder by:
* Right click (or if highlighted CMD+I) the Exchange account's Inbox Folder
* Choose "Folder Properties"
* Within the "Folder Properties" window find the "Empty Cache" section
* Click the "Empty" button
This should resolve the issue, and new email will start to arrive once syncing begins again.