Microsoft releases Windows 10 Build 21387 -- retires Internet Explorer Earlier in the week, Microsoft began to roll out the Windows 10 May 2021 Update (21H1) to all, although there are some known issues with it to be aware of. Although that feature update is now out in the wild, work continues apace on future updates of the operating system, and today the software giant brings Build 21387 to Insiders in the Dev Channel. SEE ALSO: The biggest change here is that Internet Explorer 11 is now retired as of this build. It was something we were expecting after news broke earlier in the week. Also in this flight, Microsoft is turning off the Eco mode feature in Task Manager in order to fix issues and "refine the experience".