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Privacy-Focused Proton Mail Aids FBI in Uncovering ‘Stop Cop City’ Protester’s True Identity
(www.gadgetreview.com)
This is a most excellent place for technology news and articles.
I'm pretty sure proton offers a crypto payment of some form. Which would mean if this person had used that instead of a credit card, theoretically there wouldn't be anything to subpoena.
Either way, email isn't exactly safe.