Entourage 2008 may lose the connection to Exchange server. The result is that you do not receive new email in Entourage, but no error messages are generated. 

This problem occurs because Entourage 2008 does not automatically re-connect to your Exchange account when it loses the connection if the email account is configured to use an Exchange Server back-end cluster node or a Network Load Balancing Server (NLBS) Client Access server node and a server failover occurs. Intermedia Client Access servers are running in NLB clusters and Exchange back-end servers are clustered as well, because such architecture provides better quality of service to our customers.

You may want to downgrade to Entourage 2004 SP2 to get rid of the problem. Otherwise, when the issue occurs, you can use the following workarounds suggested by Microsoft: 

  • Restart (exit and reopen) Entourage when the issue happens. The connection to Exchange will be re-established. 
  • Open another folder (for example, Address Book or Calendar). This will force Entourage to reconnect to Exchange.
  • Send new email to your own address, then go to the Outbox. When the message leaves the Outbox folder and moves to the Sent Items folder, click the Inbox folder. Entourage will download new messages.  

For more information about this issue, please refer to the Microsoft Knowledge Base article "Entourage 2008 for Mac may lose the connection to your e-mail account on an Exchange Server".