According to this story, DM News is reporting that MSN requires Sender
ID Authentication:
http://www.marketingvox.com/archives/2005/06/22/msn_requires_sender_id_authentication/
The story from the DM News website appears to be:
http://www.dmnews.com/cgi-bin/artprevbot.cgi?article_id=33158
However, I can't seem to load that page.
-wayne