Entourage copies items from a Microsoft Exchange account and stores them in the Entourage cache; if this cache becomes corrupted, it may cause synchronization problems with the Exchange server.

Emptying the Entourage folder cache is a method used to “reset” your mailbox and re-establish communication with the mail server. If you see that Entourage and OWA/Blackberry/iPhone folders and/or items don’t match, you may want to empty Entourage’s cache to fix the issue

Go to Folder Properties

To begin emptying folder cache, from within Entourage, right click (or control click) on the Inbox Folder (or other problem folder) and choose Folder Properties.

Click on the ‘Empty’ button

Click on the ‘Empty Cache’ button

Give it some time

Entourage will “hang” for a while while it empties the cache. You will have control back again once you see the folder has been emptied. Do not be alarmed when seeing an empty folder. Microsoft ® Entourage will begin synchronizing with the Exchange server and start downloading any and all mail in the folder you just emptied. Depending on the size of your mailbox, the synchronization process may take up to a few hours and may noticeably slow down your machine.