A Dangler
A dangler is that chunk of email you should’ve deleted before forwarding it. It slinks into the middle of the message like a dirty secret, and it bites someone who didn’t ask for it.
My boss forwarded me an email from his boss and included the whole lunch conversation. That was a dangler.
My mom forwarded a group chat with my sister and her ex. That was a dangler.
My teacher sent me an email with a rant about the principal. That was a dangler.