How do HTML Size, Image Size, and Pixel Height Impact Previews

Sometimes issues with previews can be explained by the HTML size, image size, or the pixel height for a project. These impact the time it takes for your email to load, and in return Email on Acid is unable to get a true snapshot of your email. You may see distorted images, partial preview returns, or no previews returned. This also means the email will take more time to load than most of your readers are willing to wait, and you may lose engagement in your campaign.


Best practice is to keep your HTML size below 102KB. If your email size goes above this, you may begin to see issues with the speed your email is loading, and this could cause Email on Acid to return no previews for your test. Visit our blog to learn more about the impact of file sizes on email.

Image Size

Best practice is to have images under 200 KB. A simple way to check for this is to run the email through Campaign Precheck. If any images are large enough to slow down your email loading speed, you will get a warning message and can optimize the image.

Pixel Height

Best practice is to limit pixel height of the entire email to no larger than 5000 to 7000 pixels. Most web clients have pixel height limit of 7000, and some desktop and mobile clients have a pixel height limit of 5000. If an email is longer than this, it may get cut off at the footer or disclaimer. It could also render fully, but take an extended time to load, hurting reader engagement.