...and there it is...
    ----- The following addresses had permanent fatal errors -----
<Billh@aaai.com>
     (reason: 550 Administrative prohibition)
    ----- Transcript of session follows -----
... while talking to backupmx1.veriomail.com.:
>>>  DATA
<<< 550 Administrative prohibition
550 5.1.1 <Billh@aaai.com>... User unknown
<<< 503 valid RCPT command must precede DATA
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