Broken placeholder images - module preview

Look in your browser console for protocol errors. Are these placeholders loaded from an http: (not https:) URL?

​@SanfordWhiteman, I have faced this issue multiple times. Sometimes, there is an issue in email template syntax but other than that I did not find any particular reason for this.

This issue usually occurs when images are loaded from a domain other than your Marketo domain. Please review the email HTML to ensure the correct domain is being used and that the images are not being served from an external domain that does not allow cross-domain requests.

Additionally, please confirm whether a new domain was recently added to the instance and whether Marketo’s default domain was used when the email template was originally created. If so, the image URLs in the email template will need to be updated accordingly.

Hi ​@sammibennett - Are you using placeholder images from an online editor or a third-party tool? If so, Marketo sometimes doesn't support these images, and they may appear broken. One solution is to upload those placeholders directly to your instance and use them from there.

Please let me know if this resolves your problem.

This usually happens when the placeholder image URL is no longer accessible. Common causes are images hosted on a restricted domain, removed assets, or a switch to HTTPS/CORS restrictions that block Marketo’s preview renderer.

Check that:

• Placeholder images are hosted in Marketo Design Studio (not external or gated URLs)

• The image URLs are publicly accessible and not blocked by auth, IP allowlists, or hotlink protection

• The placeholder isn’t referenced via relative paths or tokens that don’t resolve in preview

Re-uploading the placeholder image to Design Studio and updating the module reference typically fixes this.