I've recently seen  some MAIL (single and on lists)  coming through something
called "General  Delivery" (and with  an address of  <POSTMASTER@node>). Some
of those came from VAXen ...
As an example - here's one such a header:
*-----------------------
>Reply-To:     General Delivery <POSTMASTER@SEMAX51>
>Sender:       SAS Discussion <SAS-L@AWIIMC11>
>Comments:  This is  gatewayed mail.  Warning:  Mail may  not necessarily  be
>              returnable through this path.
>From:         General Delivery <POSTMASTER@SEMAX51>
>Subject:      Plea for help with PROC GCHART /PIE
>To:           Christian Reichetzeder <REICHETZ@AWIIMC11>
*-----------------------
There's no indication in  the header who sent that - and I  don't know if the
"General Delivery" checks if there's an address  in the text. But I think you
could end up with  some mail you are unable to  respond to directly. Moreover
the above named node  is *not* running a MAILER - and  you will have troubles
to send something to "POSTMASTER".
To state it clearly once again: there are other sites doing this...
I don't  know if  this is  the forum to  discuss this,  but since  it affects
LISTSERV I put it here first.
To summarize:
 There are nodes on BITNET which:
 a) send through some kind of "gateway"
 b) which in turn gives no indication of the original sender
 c) and  also give no  address to send to  for "General Reply"  (i.e. neither
    is the  "gateway" addressable  (because of  the long  name) nor  exists a
    MAILER or something like that which could be sent through)
Comments ?
Christian