Setting Thunderbird to default to only loading plaintext has been great for discovering sites that use trackers. Sometimes I'll sign up for a weekly newsletter,

Setting Thunderbird to default to only loading plaintext has been great for discovering sites that use trackers. Sometimes I'll sign up for a weekly newsletter, read it, but the hidden tracking isn't loaded. Inevitably, I'll get an email a few months later with instructions for unsubscribing since their tracking isn't showing that I read any of the emails.