DuckDuckGo Email Protection
spreadprivacy.com
spreadprivacy.com
https://gmail.googleblog.com/2013/12/images-now-showing.html
How about advising people to turn off remote content in emails first?
Or a more direct way to ask, what is your criticism?
Some of them are one-click unsubscribe links so I doubt DDG is going to unroll those.