Exchange 2003 help

My Exchange 2003 server will not deliver email to one domain. It used to.

Here's the NDR

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The destination server for this recipient could not be found in Domain Name Service (DNS). Please verify the email address and retry. If that fails, contact your administrator....#5.4.0
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Verified (NSLookup) that domain name resolved to correct IP.

I did a dns report (Dnsstuff.com) on the receiving domain and the only thing notiable was one of its dns servers was open. Not a big deal.

Anyone have any ideas I'm scouring through tech net and support.M$ but nothing really seems to hit.

Event ID is 3018 Category NDR Source MSExchangeTransport

Description is DNS or IP is hosed.

NSlookup says DNS AND IP are just fine.

Ideas? Anyone here ever ran across this before?

After much troubleshooting turns out there was a duplicate contact entry in AD that had a mistyped domain.

Thanks anyway for the help