I am trying to track down meaningful info on the following error and MS Exchange 2003 server.
The following recipient(s) could not be reached:
Cathleen (firstname.lastname@example.org) on 3/17/2007 2:13 PM
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
<smtp.mydomain.com #4.0.0 smtp;451 Could not complete sender verify callout>
It's only happening when the user sends to one particular domain. What I've found so far leads me to believe that the recipient's server is trying to probe my server to verify the originating email account, and my server is not responding. Some other sites suggested that it might be my server's problem.
Can anyone help?