How to Revert Back to the Original Outlook from New Outlook 365 

Professor Robert McMillen shows you how to revert back to the original version of Outlook from the new web version.
For those of you who are missing the switch back bvutton, try this advice from Microsoft:
To get back to classic Outlook for Windows
Every time you try to launch classic Outlook for Windows you'll be redirected to the new Outlook for Windows preview. You can go back to classic Outlook for Windows by selecting the toggle in the new Outlook for Windows app.
If for some reason you don’t see a toggle in the new Outlook for Windows, try these troubleshooting steps:
Make sure you try to launch classic Outlook for Windows from the Windows Start Menu, not the new Outlook for Windows. The new Outlook for Windows has a “New” tag on its app icon. For classic Outlook, select the icon without a “New” tag.
From the Windows Start Menu, type “Registry Editor” in the search box and select the Registry Editor app.
Navigate to the following path: Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences
Scroll to the bottom of the list to and double click on UseNewOutlook.
Enter 0 in the Value Data field.
Attempt to launch classic Outlook for Windows from the Windows Start Menu.