troubleshooting Question

remote host "", responded to the SMTP command "rcpt" with 550 5.7.1 Unable to relay

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zreisman asked on
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We are having an issue sending mail to the domain   Most of the time the mail goes through without issue.  Occasionally, an NDR is generated and the mail doesn't go through.  The error below corresponds the the time of the NDR.  

One odd thing I noticed while researching the issue is that the address is NOT there mail server.  The MX record for points to  I have verified this with there provider however they were not able to provide any assistance beyond that.

I thought it could be some kind of DNS issue so I changed our DNS forwarders over to and temporarily while troubleshooting with Microsoft.

Any assistance is greatly appreciated.

Event Type:      Error
Event Source:      MSExchangeTransport
Event Category:      SMTP Protocol
Event ID:      7004
Date:            3/1/2007
Time:            10:39:17 AM
User:            N/A
Computer:      OURSERVER
This is an SMTP protocol error log for virtual server ID 1,
connection #94. The remote host "", responded to
the SMTP command "rcpt" with "550 5.7.1 Unable to relay for  ". The full command sent was
"RCPT TO:<>  ".  This will probably
cause the connection to fail.

For more information,

We are running SBS 2003 with Exchange 2003 SP2
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