[rol]

Just gonna hijack this thread to mention that if you use Gnus (the other Emacs mail client) to read your email you can use the variable "gnus-blocked-images" to block any images that match a URL.

Doing

    (setq gnus-blocked-images ".*")

will block all the images in the emails.

I tested it using "https://emailprivacytester.com" and the it picked up only the DNS prefetch link/anchor which I assume are due to my ISP and not Gnus.