The Windows 10 Mail UWP app is not much loved, being quite buggy with limited capabilities.  Yet currently if you want to use the Windows 10 Share dialogue to share anything you will still only be offered to share to the Mail app even when you have full Desktop Outlook installed.

It appears this may not be the case soon, with WalkingCat finding a Microsoft extension in the Store which will add sharing to desktop Outlook possible.

The description for Microsoft Office Outlook Desktop Integration reads:

The Outlook Desktop Integration app enables sharing from Windows applications to Outlook. After installing, run any Windows application that supports sharing of content (for example, Edge) and use the Share functionality and choose “Outlook Desktop” as the target. Your content will appear in a new email message.

Unfortunately, it does not appear to be available quite yet, but you can keep an eye on it in the Store below: