When a user phones and complaints,
Outlook cannot connect to server. It's possible that Outlook is in Offline Mode. Whether you're using Outlook 2007 or an older version, go to the "File" menu and see if there's a checkbox next to Work Offline. If there is, mark it and uncheck it right away, and you should be ready to go.
If you're using Outlook 2010 or a later version, you'll need to do the following steps:
Select “Send/Receive” from the drop-down menu.
Look for the button that says "Work Offline."
Then press the "Offline" button.
You should now see something like ‘Trying to Connect.' at the bottom of
your Outlook window; if it connects, your connectivity issue has been resolved.