Several interesting changes are coming soon to Microsoft’s Mail and Calendar apps on Windows 10. In addition to an updated dark mode with a new dark grey background, Microsoft has apparently started testing the integration of a new To-Do shortcut in the left panel of the Mail and Calendar apps (via Aggiornamenti Lumia).
When you’re in the Windows 10 Mail app, this To-Do button will appear next to the shortcuts for Settings, People, Calendar. In some way, it’s like To-Do was about to become as important as these stock Windows 10 apps, and that really makes sense now that To-Do syncs with Outlook Tasks.
This new To-Do shortcut should appear in the Windows 10 Mail and Calendar apps version 16005.11001.20041.0 and higher, and you'll need to be a Windows Insider on the Fast or Skip Ahead rings to get access to this build. However, Microsoft seems to be doing some A/B testing as we're not seeing this To-Do shortcut yet on our Insider machines.