Resolution -
1. Go to Control Panel -> Mail -> Email Accounts
2. At the Email tab , Click your email account and click Change.
3. Check "Use Cache Exchange Mode" just below Server.
4. Do Next and Finish.
5. Close Account Settings Window.
6. Close Mail Set up - Outlook window.
7. Restart Outlook again and go to Send / Receive tab.
8. Now you can see an additional button "Work Offline" at the right end.
9. Click this button to toggle between Online / Offline Mode.