Can't receive emails from this domain !!

Can't receive emails from this domain !!

I can send emails to this domain but I can't receive emails from them .

They are running an Exchange 2007 Server . (Note that I have this problem only with them , at least I hope )

This is the error that they are getting 

Domain>  ciot.com
My Domain>  trendytiles.com

Is there anyway to test and solve this ? 

Kind Regards .
 

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