There's two different ways you can use it, internal and external. Internal is you sent an email that was so repulsive to the business that there is nothing that you ever earn another promotion (or more likely keep your job). They're career ending in the sense that you'll never work for that company again and thus your prior career there is over.

Or if that email gets enough public attention that it becomes public knowledge, or at least knowledge of it persists on the internet, and the content is so bad that you'll never work in your given field again. Mark Bankston, Alex Jones's lawyer, mishandled a discovery request. It was supposed to be a limited amount of data from Jones's cell phone and instead sent over an image of the phone entirely and failed to challenge the release properly. That let the prosecution prove that Jones had repeatedly lied during the trial and lead to a billion dollar fine. That lawyer will never spend another day in court, regardless if he keeps his license or not.