Exchange 2003 NDRs

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 address and all would be sorted, but that doesn't explain how this could be overlooked.

Our server received spam from (which doesn't exist) to (which doesn't exist). Our server sends an NDR to, which replies with an NDR to, which replies with an NDR to, rinse and repeat.

Unfortunately I'm not actually at the server, so cannot create the 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, what is to stop sending a mail to and the whole process starting again? Yes, I could block * (or the IP), but then what about (different domain, different IP), or I obviously cannot block *.com.
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TalkExchangeConnect With a Mentor Commented:
This should be helpful

Exchange queues fill with many non-delivery reports from the postmaster account in Small Business Server 2003
VampireofdarknessAuthor Commented:
I had thought I had enabled sender filtering, connection filtering, etc... but apparently they had been disabled.

Re-enabled in order for the 'reject recipients not in directory' option and all is well.
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