Once the apps reach end of support later this year, Microsoft warns that users who haven’t moved to the new Outlook app “will no longer be able to send and receive email using Windows Mail and Calendar.

Microsoft will discontinue the built-in Mail and Calendar apps in Windows 11 after December 31, 2024, urging users to switch to the web-based Outlook app instead.

If you're still using either of these apps, you'll need to switch to the new Outlook or find alternatives soon.