Because we are asked so often, we decided to study dozens of successful, historical email campaigns and find the common denominators of a successful HTML email design.
Note: This assumes that the recipient list is good, the server reputation is great and the subject line/pre-header gets readers to open the email (covered in a different topic). Of course, designs can and will vary. Some folks use email template designs and other build from photoshop to HTML, but the common structure outlined below appears to be the most productive from our review of past email campaigns over the last couple of years.
There are other considerations and best practices outlined here.
Note: the image with callouts is clickable and opens a larger image.
The key points summarized below -