If your Entourage Mac for Exchange Server stops synchronizing new e-mail from your Exchange server it might be caused by a corrupt inbox cache.  A customer was having a problem where their Mac was not synchronizing with their Exchange server and the inbox cache was the culprit for them.  The solution is to go to the properties of the mail folder and select to clear the cache.  After doing so, synchronization will download all email from the Exchange Server.  I found the solution for this problem posted on the following site: www.macwindows.com/entourage