Here it is:
A non-delivery report with a status code of 5.4.0 was generated for recipient rfc822;firstname.lastname@example.org
elli.mil (Message-ID <BBDFE4B40DD4AE4F8D79DC4B8
Causes: This message indicates a DNS problem or an IP address configuration problem
Solution: Check the DNS using nslookup or dnsq. Verify the IP address is in IPv4 literal format.
For more information, click http://www.microsoft.com/contentredirect.asp
Very odd I have a couple of the same events but from different email addresses in the event log. These are legitimate as well. Any ideas? I see no problems in our DNS config...