When handling the marketing emails with images and formatted texts, its better to make use of the feature to edit email in full-screen window. Sharing this simple yet much useful feature for those who are not aware of it already.
To access this mode, click on the expand icon in the email form.
Clicking on this icon, will open the email content editor in full-screen mode. To go back to the normal view, click on the collapse icon in the expanded editor:
Hope this helps!