Perhaps someone can help / explain what is going in. We seem to be stuck in an infinite NDR loop. I know I could create a email@example.com address and all would be sorted, but that doesn't explain how this could be overlooked.
Our server received spam from firstname.lastname@example.org (which doesn't exist) to email@example.com (which doesn't exist). Our server sends an NDR to firstname.lastname@example.org, which replies with an NDR to email@example.com, which replies with an NDR to firstname.lastname@example.org, rinse and repeat.
Unfortunately I'm not actually at the server, so cannot create the email@example.com address right now, which means an email every ~1-3 seconds is being sent and received, constantly. That is obviously no good for the server's disks.
Now, assuming I create firstname.lastname@example.org, what is to stop email@example.com sending a mail to firstname.lastname@example.org and the whole process starting again? Yes, I could block *@other.com (or the IP), but then what about email@example.com (different domain, different IP), or firstname.lastname@example.org? I obviously cannot block *.com.