Sometime some friend ask me how to let Windows 10 choose the more appropriate app for you when you click on a file with a specific extension (e.g. a .jpg photo).
Windows 10 has its default apps but possibly they are not all the ones you would like. For example, you would like to use Outlook to open an email and not the Mail app as it is configured by default.
In particular, if you use Outlook desktop application as your preferred email client, it is annoying to get Mail app open every time you click on a new email notification from the Notification panel. However notifications in that panel comes from all the running app/applications: so, at the reception of a new email, you will receive a notification from both Mail and Outlook 2016. Note that the notification from Outlook 2016 will arrive only if that desktop application is running, while the one from Mail app comes anyway, even though that app was not launched before.

A notification from Outlook 2016 will arrive only if that desktop application is running

The notification from Mail app comes anyway, even though that app was not launched before

Furthermore note that you could use Outlook app, from a Office 365 subscription, as a mail client and not the free Mail app, usually available on every Windows 10 device.

In the following the few steps to let for example change the default application for email.
The procedure is very easy but I notice that possibly it should be repeated after some major Windows 10 update.

The same page could be reached also from the Control Panel desktop application, going to Programs section and then to the Default Programs one:

Clicking on the proper section (e.g. the Email one), you can then choose the default application: note that anyway, right clicking on a file, you can always choose a different application to open whatever file.