Mailflow has stopped since March 26th 2008.
Third party blacklists are enabled, and relays.ordb.org is present in the list. Any message sent to a domain protected by Symantec AntiSpam products gets a 550 5.2.1 or 554 response.
The messages look like:
This blacklist is no longer in use. It went out of service in December 2006.
Remove relays.ordb.org from your list of 3rd party blacklists.
ORDB.org Going Offline: http://it.slashdot.org/article.pl?sid=06/12/18/154259&tid=230
Long-Dead ORDB Begins Returning False Positives: http://it.slashdot.org/article.pl?no_d2=1&sid=08/03/25/2124224