Sorry for late response but reply wasn't working.
There were no updates availabe, and then I was using latest w10 mobile preview for lumia 820. So not newest, because 820 didn't get w10 mobile officially.
Now i have lumia 650 with latest w10 mobile. First I was on dutch region, and the mail app showed inbox as default. After changing to english region default changed to draft again. But if that is really related i'm not sure. I did try if default changed to inbox again when changing to dutch region but that's not the case.
So again I'm stuck again with draft box as default, also with no posts in that draft box