Interesting, but can we trust Ugly Email. I also wonder if something like this could be implemented by an ad or script-blocker.
I think you made a good point (re: trustworthiness). It can be, as they're not much different from usual beacon tracking. Also disabling image load will prevent this (in theory, or as long as Google haven't whitelisted those tracking pixels). Also some email track your mouse cursor, so disabling javascript is good counter measure against it.
