This is something I've been wondering about for quite some time, particularly given that large providers can hash the images and conserve storage space by storing only a single copy of the image per hash.
I would suspect there are privacy implications of google caching what's behind every image tag in an email, in addition to the massive traffic / CPU spike such a thing might cause to retrieve the image and hash it, particularly for a very large email campaign. (But I don't know).
I would suspect there are privacy implications of google caching what's behind every image tag in an email, in addition to the massive traffic / CPU spike such a thing might cause to retrieve the image and hash it, particularly for a very large email campaign. (But I don't know).
[Edited to include this link, which I found in another comment here] "Gmail will now serve all images through Google’s own secure proxy servers." https://gmail.googleblog.com/2013/12/images-now-showing.html