It happened to me in a large company I worked with. Someone, probably an admin sent an email to the entire company, literally tens of thousands of people in the

It happened to me in a large company I worked with. Someone, probably an admin sent an email to the entire company, literally tens of thousands of people in the "To:" field. Of course, a few of them replied-all, then others replied to tell people to stop replying, etc... The server couldn't follow and mail couldn't be delivered fast enough, prompting even more replies. Email unrelated to the incident took 30 minutes to come through. Admins had to intervene, and the servers were down for about 4 hours, everything related to the incident was deleted server-side, and probably blacklisted too. The client couldn't do much, we didn't even get that many emails (a few dozens at most) since the server couldn't deliver them. It was a very expensive email for sure.