Possible cause

Your device does not have a default email client set.
Solution: The device needs to first have a default email client set under default MAILTO protocol options on their device, or set a default application to handle email (instead of an internet browser.

Solution

Change MAILTO protocol on your device.

Windows 10 users

The following works for Windows 10 users and describes changing the default for mailto protocol from Google Chrome to your email client (e.g. Outlook)

1. Open the Windows settings section, and choose Apps followed by choosing Default apps from the left-hand navigation (or click start and type default apps before selecting Default Apps).
2. At the end of the page select Choose default applications by protocol.
3. Find MAILTO in the list of protocols available and change it to the email client that you want to use. (The screenshot below displays what has happened after you complete this step (3) and select Outlook.)
4. If I now change my default app by protocol setting for mailto to outlook (click on Google Chrome and then pick Outlook instead), it will look like this...

Change default email application on your device

Windows 10 users

Instead of changing the mailto protocol default, a user can instead change default application for Email from an internet browser to email application. To do this:

1. Open Windows settings section, select Apps followed by choosing Default apps from the left-hand navigation (or click start and type default apps before selecting Default Apps).
2. Next to the heading for email, select the app displayed under the heading of Email and pick the email client of choice.