Why Am I Getting Undelivered Mail Returned to Sender Emails?
I am getting numerous Undelivered Mail Returned to Sender emails from email@example.com. Here is an example and I followed the link to error code meanings for CXSNDR and found that it appears to be a problem with Cox domain. The email also listed 552 which is a list of prohibited file types. However, none of my emails included a prohibited type of attachment.
The other problem is that the returned mail message does not identify to whom the returned email was sent to so there is no way to know whose email was returned.
Can anyone help explain and resolve this Undelivered Mail Returned to Sender problem?