I recently got a call from a client who was having a hard time connecting to their Exchange 2003 server. They kept getting a “disconnected” error. I told them to ping the exchange server and other computers on the network to see if they would get a response, they did and everything looked fine. I then asked if they had done anything different lately. It turned out that this particular computer had static IP settings and they had removed the gateway IP address because it was interfering with a specific website. So I told them to plug in the IP address of their gateway and presto, Outlook started communicating with the exchange server. Obviously, they did not have that problem with Outlook 2003. It only started with the upgrade to Outlook 2007.
So if you get a call from someone complaining that they cannot connect to their exchange server with Outlook 2007, have them check to make sure there is a gateway address in their IP configuration.