At work, we had a mail loop once; a girl from accounting had ordered toner for our printers last thing before she went on vacation and enabled an auto reply on her mailbox.
Five minutes after she left the office, the order confirmation arrived, sent from noreply@random.office.supplies.whatever. Her mailbox sent an auto-reply. Our mail server sent her an error message, telling her that her reply had not been delivered. To which her mailbox happily replied with the same auto-reply mail...
When I walked into the office on Monday, her mailbox had accumulated around 50,000 of those mails. Fun times.
In the early days of "exchange" ... the email client. I discovered auto replies.
Very first thing I thought of was "What if two clients have auto replies set?"
So naturally I set one up, my cube neighbor set one up. I sent an email to my cube neighbor ... and fairly quickly email was down company wide for a good afternoon.
IIRC rules such as out of office (I'm not sure "rules" really existed). Were client side only... the server didn't have the option (or at least it wasn't automatic) to evaluate bad rules / out of office.
I once (accidentally) setup a mail group with itself as a member.
Everything was fine until the first message came in, and a few minutes later I hear "Uh, why do I have 5,000 new emails?" "Woah, I have 9,000", "Oh, mine is at 15,000 now!".
I don't remember what it got up to before we managed to get into the now-very-slow mail server to fix it, but it was in the hundreds of thousands. Luckily it was only internal mailboxes.
I've got a client with an automated ticketing system that loves to get into mail loops with our automated ticketing system. They keep confirming that they've received a reply or update to the previous ticket and a single inquiry can rattle back and forth dozens of times.
Yep, had the same thing happen after I implemented an automated mailing process at work. Luckily the ticketing system we hit was slower and I caught it around 6k emails the next day.
If said Jira server is backed my MySQL in the default “UTF8” mode that isn’t actually UTF8. Tell your Jira admins to switch to Postgres or Jira Cloud and all will be well. The same thing happens to Wordpress installs all the time, sadly.
Five minutes after she left the office, the order confirmation arrived, sent from noreply@random.office.supplies.whatever. Her mailbox sent an auto-reply. Our mail server sent her an error message, telling her that her reply had not been delivered. To which her mailbox happily replied with the same auto-reply mail...
When I walked into the office on Monday, her mailbox had accumulated around 50,000 of those mails. Fun times.