How do I set Outlook as default email reader?

I'm using Outlook 365 as my email reader on my MacBook Pro, running High Sierra. I want to set Outlook as the default reader, but the instructions I've found to do that online aren't working. They say to open the mail app, click Outlook Menu>Preferences>General and set Outlook as the default email reader. When I follow this path, however, the only options are to "Show all account folders," "Hide On My Computer folders," and Personalize my Office theme (see photo).

Any other suggestions?