If Google was evil (but in reality it's not), it could have forged and signed an email from john.smith@gmail.com with valid DKIM, sent on other mail servers or not (since we talk about leaked emails, we just need a file), when in reality the Google user john.smith@gmail.com never sent that email. To me, John Smith could have plausible deniability in court, depending on if everyone trusts Google to be 100% reliable. If the stakes are higher than what the company would risk to lose if found to have forged the email, what's stopping them?
