Open Settings

Select Apps, then select Default Apps

In the search bar under “Set defaults for applications," enter the name of the email application that you’d like to use as default e.g. Outlook

Choose from the list of file or link types that you would like to set to open with your selected default app.

Example: 
MAILTO - If you set Outlook as the default app, clicking an email address in a web browser will automatically open Outlook. Allowing you to compose an email and send it to that address.

Select Choose a default, then select the application that you want to use