The MAILER agent at the receiving site did not "like" one
of your addressees.  It's _modus operandi_ is to abstract
the recipient address from the RFC821 headers and append
a BCC: to it since it did not show up in the RFC822 fields.
 
It then mailed it back to the list (a "boo boo") or to you
(a smaller "boo boo").  If the former, you should delete
this user ASAP; also check your SEND= options and/or FILTER=.
 
The reason for the original bounce is either a non-existent
userid, or a mail administration at the recipient's host.
 
/Pete Weiss at Penn State