A new build of Windows 10 has leaked onto the internet today. Build 10051 adds a few new improvements to the latest official build of 10049, including a new Mail and Calendar apps (spotted by @rlinev), as well as various minor improvements throughout the operating system.
We highly recommend avoiding this build until more details become available. WinBeta will not provide download links either! Hang tight while we learn more about 10051 and what new features it contains, and if it will affect your chances of updating to the latest official build.