Outlook 2003 / Exchange 2003 cached mode

We run an exchange server and about 40 Outlook 2003 clients in Cached mode. If our exchange server is down for any reason, Outlook goes into Offline mode. When the exchange server comes back, most Outlook clients go back to Online. However, one or two will not. It is not the same clients each time either. How can I make sure Outlook goes back online when our Exchange server is up and running?

Thanks