I see from the Google Request for Permission interface that Signal wants to "View your email message metadata such as labels and headers, but not the email body

I see from the Google Request for Permission interface that Signal wants to "View your email message metadata such as labels and headers, but not the email body". That's way too sensitive for me to give away in exchange for uncertain benefits. I realize that I've given this information to Gmail already. But it's not hard to concoct some very plausible bad scenarios of what could happen with this data if I said Yes.