The image in my email broke! How do I fix?
Broken images in emails are often rendered when the URL to the image is missing on the server's side. Usually this means that the image was added to the Snippet by dragging and dropping it from the desktop or by clicking "Insert Photo" in the Snippets Manager.
The best way to make sure the Snippet image doesn't break is by hosting the image publicly on an image hosting website. Upload the public image to the Snippet by clicking on "Web Address (URL)". The previously linked article will also explain how you can use a Google Doc to host the images if you don't have a hosting site.
If your image is broken when trying to send a Mail Merge, try hosting the image publicly, then adding to a Snippet. When you setup the Mail Merge, insert the Snippet with the image into the email draft.