I'm not sure I want to open this can of worm here, but this is one of the appealing properties of differential privacy: there is a quantitative bound you can invoke ("we will mine at most eps-dp from your emails, in exchange for this tasty cookie") and then you don't have to have a complicated discussion about which types of PII they ripped from your email, metadata vs non-, and other increasingly meaningless distinctions.

Differential privacy also has the nice property that it works like a fungible currency: it is additive, so even if you hand out x, y, and z units to different folks, they collectively can't spend more than x + y + z units, no matter how clever they are. In principle this could help folks determine a value for their sensitive data, and perhaps set up decent standards for people to value their own privacy (e.g. "selling 0.1 units of differential privacy from your email could shift your health insurance premiums by 10%").