Mail bounce back message

I get a mail bounce back when I send to a certain single domain only:

Server refused mail at MAIL FROM - 530 5.7.1 Client was not authenticated

I do not receive a bounce back from any other domain.
Is the configuration issue on the recipients end?
Using Microsoft Exchange Server 2010, Outlook 2010 and Cisco IronPort mail gateways on the sender side.
Any information appreciated.
fsaiexpertFSAI ExpertAsked:
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Amit KumarCommented:
Make sure you have added affected domain in Accepted domain for Ironport and Exchange. Seems they are denying to route e-mail using affected domain.
Alex GreenProject Systems EngineerCommented:
not your problem, their problem, get them to whitelist your domain or exchange.

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fsaiexpertFSAI ExpertAuthor Commented:
I have Anonymous Users allowed for my MS Exchange and Cisco IronPort so didn't think it was sender problem.
Also sender only having issue with one specific domain.
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Alex GreenProject Systems EngineerCommented:
I assume you've locked it down to IP right?
fsaiexpertFSAI ExpertAuthor Commented:
I assume you've locked it down to IP right? - Please explain?
Alex GreenProject Systems EngineerCommented:

You need to lock down your exchange so only specific IP addresses can communicate anonymously. Otherwise people can you use as a relay
fsaiexpertFSAI ExpertAuthor Commented:
Thanks for clarification and agreed - we only use 2 Mail Gateway IP Address to relay from the internet
fsaiexpertFSAI ExpertAuthor Commented:
Thanks for assisstance
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