Connection indicator located in right hand corner displaying Offline status.
Okay, I admit I should have given Clippit the boot a long time ago. And yes I know Clippit was detested among most users as intrusive and annoying. I cannot remember when I activated Clippit but I do know I never got irritated enough to turn it off...until now.
How did Outlook become offline if I did not change its setting? I was told that if there is a long enough disruption in the connection to the Exchange server, Outlook could switch to an offline status and remain like that until you reconnect using the connection button in the lower right corner, or by selecting File / Work Offline. We had a couple of email disruptions the past couple of weeks which might have triggered the Outlook to disconnect from Exchange.
So when I clicked the Work Offline command, the check mark disappeared (which means it was deselected) and Outlook quickly connected to the Exchange server. My other mailboxes were accessible, and all was well again.