A co-worker at the city-government just chose the wrong mailing list and send an e-mail to EVERY SINGLE emlpoyee (about 20'000 people, including our police-department, hospitals, councils etc.).
Within A MINUTE hundrets of people responded to the mail by using the "reply all" button, pointing out that this mail obviously wasn't meant for them.
After another minute the same douchebags sent another mail (of course using the "reply all" button AGAIN), asking to be removed from the mailing list and stop spamming them.

Even two hours after blocking the mailing list immediately, our mail servers still are processing all those damn mails.

RIP exchange servers
RIP inbox
RIP faith in humanity

Edit: typos