http://www.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/pages/online-privacy-nonprofits
Not tracking email open rates can, unfortunately, sometimes cause list “hygiene” problems, because it becomes difficult to know whether email subscribers on your list are still interested. You can send occasional emails to ensure subscribers want to receive emails, either using open or click tracking, and informing people that the purpose of that specific email is to determine active subscribers.