Windows

1. From the Start menu, search Default Apps.
   
   
2. Click on the mail icon and choose the preferred e-mail application.

macOS 

When using the Email Team feature from a macOS device.

1. Open Apple Mail app.
   
   
2. Click on Preferences under the Mail menu item (top left).
   
   
3. Make sure the default email reader is set to Microsoft Outlook or the preferred e-mail application.