On Exchange 2010 some people that reply to one of our emails get an error message of
Delivery has failed to these recipients or groups: firstname.lastname@example.org The e-mail address you entered couldn't be found. Please check the recipient's e-mail address >and try to resend the message. If the problem continues, please contact your helpdesk.
But the receiving user gets the email regardless of the error message the sender is receiving. This problem started shortly after we upgraded to exchange 2010.The sender and receiver are in different domains. What is causing the error message and how can I stop it from happening?
For the full error message see the following link http://pastebin.com/WfYbBDBH