Haven't seen precisely what you describe, Geert, but something similar.
A brain-dead site started sending errors to the listowner-list address
rather than the Errors-to: address.  And it sent them with a From:
field of listowner-list. Send something to that address and you get
an "automagic" reply that the message has been submitted to the listowner.
Since the From: field said listowner-list, guess who got all these nifty
notes?
 
When I tried to deal with it personally my messages started coming
back as bounced mail, but with *my* address in the From: field
(error message From: me   To: me ).  They'ld  repeat the same thing
every four to six hours.
 
I never could get the people to say anything, but found an address that
got results, after about two weeks.  Every time I got one of those things
I just bounced it back to that address.  They never did say anything, but
I did get the garbage stopped, once I found the right address.
 
My impression was it was just a brain-dead system, nothing malicious.
 
Douglas
       Douglas Winship   Hays County, Texas  [log in to unmask]
                    Secondary AUTOCAT Listowner
                              MEDLAB-L