We've recently been put on two blacklists so I am looking in the Exchange 2010 queue to see if anything fishy. I see over 100 spam email domains with DNSConnectorDelivery in retry states. All the emails seem to have Undeliverable in subject. One such example below:
Subject: Undeliverable: Ends Today! Get Your Free Gift
Internet Message ID: <email@example.com>
From Address: <>
Size (KB): 10
Message Source Name: DSN
Source IP: 255.255.255.255
Date Received: 5/22/2013 3:21:52 AM
Expiration Time: 5/27/2013 3:21:52 AM
Queue ID: mail1\160283
The Last error is 451 4.4.0 Primary target IP address responded with: "421 Unable to connect." We are not an open relay and we use Postini to filter our inbound email. I have installed AntiSpam on our Hub Transport and enabled Sender and Recipient Filtering to assist.
The emails show no sender and no source IP so I don't understand how they are ending up in our queue.