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5.1.0 - Unknown address error 550-'5.7.1 Unable to relay username@clientdomain.com

CMBeck asked
Last Modified: 2012-05-08
All of a sudden one of my clients has been having clients getting bounce backs that have this information in it.

5.1.0 - Unknown address error 550-'5.7.1 Unable to relay username@clientdomain.com

The server has no errors in the event viewer.  There does not appear to be anything wrong with exchange, I even checked with the mail filtering and that appears to be working fine.  I have even checked the receiptant policies just in case they have changed and they haven't.  I am running out of opitions and I am losing my mind on this problem because it just happened all of a sudden and it is not constant.  I need help BAD.
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