Microsoft announced last year that it would be retiring the Windows Mail & Calendar apps in favor of the new Outlook at the end of 2024. As of January 1, these apps are no longer functional and will refuse to send or receive any more emails.

Designed to replace the current Mail and Calendar apps, the new Outlook can only be removed after it's been installed.

Microsoft will automatically install its new Outlook client on Windows 10 PCs with next month’s Patch Tuesday update.

Microsoft will force install the new Outlook email client on Windows 10 systems starting with next month's security update.

The good news is that the February update which brings the new Outlook doesn't strip out the old version of the app, so you can still use that.