Getting error 550 "The recipient cannot be verified

[max8699]

We have a client that receives their e-mail through our exchange server, mail is sent to them at boss@thisdomain.com.au comes to us we then forward it on to boss@theredomain.com.au. Now sending mail to them from inside our domain is fine that all works however if someone from outside the domain, ie joe at his pc at home needs to send an email to these people, it gets bounced straight away with the error message
----- Transcript of session follows -----
... while talking to theredomain.qld.edu.au.:
>>> DATA
<<< 550-"The recipient cannot be verified. Please check all recipients of
this
<<< 550 message to verify they are valid."
550 5.1.1 <boss@theredomain.qld.edu.au>... User unknown
<<< 503 valid RCPT command must precede DATA

Any ideas what is happening? Worked fine as of last Thursday 4/1/2007 but not now.
Regards
Max

 

[brontosaurus]

Any changes made to DNS by either you or your ISP?

 

[max8699]

turned out the people hosting the web site for our client decided to setup their own ip addresses pointing to there own servers including the mail. so of course when somebody sent a e-mail it was getting to the server and saying no such address exists.
However No body want to take the blame for it though.
But it works now, so all are happy :-D