Hi Thomas ! I just ran a few tests, and here’s what I observed for background images blocking. I tested using the HTML `background` attribute, and the `background`and `background-image` properties in CSS.
- Gmail removes the path of the image inside the CSS properties. So `background:url(foo.jpg)` becomes `background:url()`.
- Yahoo removes the `background` attribute, as well as the `background`and `background-image` properties in an inline `style` attribute.
- The old Outlook.com replaces the URL of the image by the same grey image it uses for the `<img>` tag.
- The new Outlook.com (and Office 365) replaces the HTML `background`attribute by a `blockedimagesrc` attribute.
- AOL replaces the HTML `background`attribute by a `removedimage__f58c7fd5–1234–5678-bf5c-12e2e4b5f678__background`attriubte. But it doesn’t block background images in CSS.
In practice, these different way to block background images don’t really matter because it doesn’t affect layout (contrary to <img> blocking).