Sometimes it can be very tricky trying to debug issues with Microsoft Exchange Server and Outlook clients. There are various reasons why a client won’t properly connect to the Exchange server. This can include: incorrect settings, network issues, routing problems, packet loss etc.

Another problem that can cause intermittent errors when connecting to exchange server, is the Subnet Mask. If all clients are able to connect, except one, try checking the subnet mask. An incorrect subnet mask will cause problems with connecting to the Exchange server. The connection errors may not be consistent and in some cases it may work.

To check the subnet mask of a client computer in Windows 7:

Control Panel -> Network and Sharing Center -> Change Adapter Settings

Right click on your network connection and select “Properties”. Now click the protocol you are using, most likely IPv4 and click “Properties”. here you can configure the subnet mask. This will only be applicable if you are using a fixed IP address.