[ejenner]

Worked it out - has been bugging me for a while but only just got a chance to look at it - shows what you can do when you put your mind to it..

Found that this is a Windows Firewall problem (as is the case with so many things these days) - I just added Outlook to the exceptions list.

The problem is caused because the Exchange server sends it's new mail notifications (guess this function tells the client to display new messages and shouldn't be confused with the box that appears when a new message arrives) using a different port to what is used for all other Outlook / Exchange communication. So even though Outlook communicates with the Exchange server in most respects - it does fail to receive the new mail notifications. This communication occurs on a UDP port (not sure which one) and involves some IGMP traffic also. Tried making a specific exception in the client firewall settings but I couldn't find enough information to make the rule work properly so I just excluded Outlook.exe - but only for traffic passing between Outlook and our internal Exchange server.

If anyone can locate the information for specifically configuring the port settings to allow the new mail notifications (and new messages to appear as they arrive) then post it here. Completely excluding Outlook isn't an ideal way to implement the new firewall technology - I suspect Microsoft will fix this in the final release - does not effect Outlook 2003.

I also found that this problem could appear when ISA 2000 server is filtering traffic between server and client.

The fix was a Microsoft one - although it didn't refer to Service Pack 2 - I think it is applicable and more relevant because the firewall is automatically turned on after installing SP2.