I actually wrote a little tool to help test this: https://github.com/kale/image-cache-logger https://github.com/kale/image-cache-logger You'll see that it in f

I actually wrote a little tool to help test this: https://github.com/kale/image-cache-logger https://github.com/kale/image-cache-logger You'll see that it in fact does get cached by Gmail, but only for a limited time.