One of my users just started getting NDRs, supposedly  due to this error whenever he attempts to send messages to anyone outside of our domain.  As far as I can tell, the issue is only impacting this single user.  When I see him again, I'm going to have him try sending a message from another machine via OWA.I haven't done anything on the server side that should have any impact on his specific account.  A sample part of an NDR follows.  Thanks for any ideas:
 

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user@gmail.com on 1/27/2009 1:14 PM

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MSEXCH:MSExchangeIS:/DC=edu/DC=msu/DC=rcpd:ourServer



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