if I understand it correctly, user's prompt does not need to be related to the specific malicious email. It's enough that such email was "indexed" by Copilot and any prompt with sensitive info request could trigger the leak.
Of course you need to use the feature in the first place, like summarize an email, extract content from a website,...
However, this isn't the first zero-click exploit in an AI app. we have seen exploits like this in LLM apps of basically all major AI app over the last 2+ years ago (including Bing Chat, now called Copilot).