“If your email is split into columns, place important content, images, or call-to-actions on the left. If your email doesn’t have columns, be sure to left justify your content.”
Nielson Norman Group states that web users typically spend 69% of their time viewing the left half of a computer screen or web page. This means that you should be designing your emails with this fact in mind. Pay attention to columns, content placement, images, etc., and make them significant and heavy on the left.