Until recently, the non-accepted domain report (available from the Mail Flow dashboard), correctly reported only non-accepted domains. For example, a misconfigured scanner trying to send from an email address that a copier engineer thought up on the fly.
Now it also appears to include non delivery reports, with a hop count exceeded message. This appear to always be for when a user exists but does not have a mail box. This is making the report much more difficult and time consuming to interpret, reducing its effectiveness.