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 firstname.lastname@example.org address and all would be sorted, but that doesn't explain how this could be overlooked.
Our server received spam from email@example.com (which doesn't exist) to firstname.lastname@example.org (which doesn't exist). Our server sends an NDR to email@example.com, which replies with an NDR to firstname.lastname@example.org, which replies with an NDR to email@example.com, rinse and repeat.
Unfortunately I'm not actually at the server, so cannot create the firstname.lastname@example.org 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 email@example.com, what is to stop firstname.lastname@example.org sending a mail to email@example.com and the whole process starting again? Yes, I could block *@other.com (or the IP), but then what about firstname.lastname@example.org (different domain, different IP), or email@example.com? I obviously cannot block *.com.