When you use Outlook with an Exchange Server with MAPI, server connectivity is needed for directory queries as well as message store access. A quick way to check which servers Outlook is communicating with is to use the Microsoft Exchange Connection Status dialog box.
In Microsoft Office Outlook 2007 or Microsoft Office Outlook 2003 hold the CTRL button and right-click the Outlook icon in the task bar, select Connection Status. Outlook will automatically find another Global Catalog server on its own, if the one it's connected to become unavailable. This is a quick way of verifying that Outlook is establishing client-server communications. The Reconnect button will force Outlook to attempt to find a Global Catalog server and its mailbox server. If it's already connected to those, it will disconnect and reconnect (as the button name suggests).