If you're like me, you loathed Windows 10 Mail conversations view. When 10 originally came out, there was no choice, we were all forced to use it. It's one of those features that quickly got under the skin and there were a lot of complaints about it. Well, good news! If you have been keeping your system up to date and patched, then you can now turn it off.
Click on the small gear at the bottom left of the screen.
A window will slide out on the right-> click OPTIONS -> VIEW SETTINGS -> SHOW MESSAGES BY CONVERSATION and push the slider to OFF.
That's it. Job done.