Having a preview next to text editor, should it be on the left or right side?

I'm trying to design an email text editor that has a preview window next to it. Should the preview be on the right or left side of the editor? My reasoning is that the preview should be on the left side because majority of people are right-dominant so the immediate actions (editor) should be on the right, but I've seen editors with the preview on the left so which is more natural?