Try doing this, right click on your Start button, select Command Prompt (Admin), click on Yes, at the Command Prompt C:\WINDOWS\system32> type in sfc /scannow and hit your Return/Enter key
When it's done close all open programs and reboot your PC, that fixed it for me, make sure you have a space after sfc and the /
Credits to A.USER. The original thread is here:
http://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_web/cannot-send-emails-in-windows-10-build-10140-via/ebb32467-67c7-41e9-b161-4ab4185b19d1
Hope it solves your problem.
BTW MS you should fix bug anytime soon. This wasn't exactly the most welcoming reception to W10...
