I'm using a fluid/hybrid design for my email template. The email I'm working on has multiple photographic-quality imagess, so I want to optimize them for retina display.

I basically have three sets of images: one standard (for desktop); one high-res (for retina); one for mobile. (The image/content is actually different for mobile -- which is a separate issue).

Through media queries, I'm hiding the 'standard' image and attempting to add a bg image in its place. However, I can't seem to make the bg image fluid (width:100%, height:auto), as the container is not a fixed size. Is there a way to do this through media query/CSS? I've been searching on this topic but haven't found what I'm looking for. Or perhaps there's another approach that I'm overlooking...

Thanks for any help!