To enable new mail notification, Exchange Server relies on routable addressing between the Outlook client and the Exchange Server. In the presence of a network address translation (NAT) device (such as ISA Server) between the client and the Exchange Server, new mail notification will not function properly.

New mail notifications sent to the private address are dropped, because these notifications are unsolicited inbound UDP packets not associated with some previous outbound flow. The ISA Server Exchange RPC filter does not know how to access the registration payload to change the client-registered address. Currently no NAT editor is available that knows how to access and change client-registered addresses.

The Outlook client also receives mail notifications during other communications with the Exchange Server. However, if an error in any of the RPC packets occurs (this can happen when RPC is carried over the Internet), the Outlook client does not receive the new mail flag at the end of the packet. To work around this limitation, do the following:

• For Outlook 2000 periodically press F9 to check for new mail
• For Outlook 2002, configure a polling interval.