Although the larger banners get more click throughs, placing a large image above the fold may take away from instantly viewed content, especially when users have not downloaded images.
Tracking banner ad’s individually is important in understanding the level of user engagement and making judgments about if and where to place ad’s in the future.
Studies have shown that movement does generate higher click through rate but some moving or flashing banners can come across as spam and can take a while to load.
Colors and text should complement the newsletter but should still stand out, the advertisement or image should work with the content.
If you are sending out to different emails different banners may be more relatable to each group. Target each group to receive the appropriate advertisement as you would with the newsletter content.
Incentives like give-away, discounts or gift are good for attracting your reader’s eye but you don’t want an ad’s call to action to prevent the reader from exploring mailer content.
Banner advertisements are a good way to spread brand awareness, promotion products, and drive traffic to website. Just remember - This could be the first step in attracting a customer but it is your website that will be the final step for converting.