We are having an issue with email one customer
We are getting the following message
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
retry timeout exceeded
------ This is a copy of the message, including all the headers. ------
I can see the email pass through exchange and our spam filter and then we receive this message.
If we use an external email (gmail) we have no issues emailing the customer.