The IETFHDR setting is named for the Internet Engineering Task Force.
It specifies that mail from the list to the subscriber should look as
much like mail from a "normal" Internet mailing list as possible (as
opposed to looking like mail from a LISTSERV list).  This includes
leaving in some headers from the original mail that LISTSERV would
usually strip out, using the owner- convention for Sender:, and not
rearranging the From: and To: headers.
 
It is this last aspect to which the MCIMAIL gateway seems to object,
if indeed IETFHDR is relevant to the problem at all.  (The MCIMAIL
gateway has been doing some strange things lately.)  The message you
included indicates that it is unhappy with the From: address, perhaps
because it appears that this user is sending mail to herself but not
through her "current relay account".  If the other MCIMAIL subscriber
gets this subscriber's submissions, it is probably this apparent loop
that is the problem.  If they bounce to you (which I gather they do
not), it might be something else.
 
WERTSJ probably should just forgo the REPRO option.
 
Mark R. Williamson, Rice U., Houston TX; [log in to unmask] or @RICEVM1