I have a user who gets a NDR for one particular person each time she sends an email to them. Below is the NDR that is returned.
The following recipient(s) could not be reached:
email@example.com on 9/6/2006 3:52 PM
You do not have permission to send to this recipient. For assistance, contact your system administrator.
<exchange.domain.com #5.7.1 smtp;550 5.7.1 Requested action not taken: message refused>
Now I tried sending a message to this person and it went through successfully so I know its not a problem with the address. My user used to be able to send to this person now everytime she send she get the same message as above.