Hank, I'd  be very  interested in how  DATABASE's code  would have
detected the  loop.  The loop  succeeded in evading all  of LISTSERV's
loop detection code, which is pretty good in it's own right.  LISTSERV
detects several conditions which indicate a potential loop, including:
 
   1) From: is the local mailer;
   2) From: contains one of the words MAILER, SYSTEM, and DAEMON;
   3) From: is the mailer listed in XMAILER NAMES for the source node;
   4) From: is the mailer listed in DOMAIN NAMES for the source domain;
   5) Sender: contains one of the strings <listname>@<listnode>,
      <listname>%<listnode>, and <listnode>!<listname>;
   6) Subject: is UNDELIVERED MAIL or RETURNED NETWORK MAIL.
 
    In addition,  any user  sending 10  invalid commands  in a  row to
LISTSERV will  have access to  LISTSERV suspended, until  another user
(any other user) tells LISTSERV to re-instate access.
 
A sample of the mail in question was (after distribution by the list):
------------------ Start of included file UUCP     MAIL        -----------------
Received: from BITNIC(MAILER) by RUTVM1 (Mailer X1.23b) id 7768;
          Wed, 22 Apr 87 02:32:07 EDT
Received: by BITNIC (Mailer X1.23b) id 6024; Wed, 22 Apr 87 02:33:28 EDT
Date:         Tue, 21 Apr 87 09:43:01 PDT
Reply-To:     UNIX-to-UNIX Copy <CMCL2!RUTGERS!SRI-SPAM!CSI!UUCP>
Sender:       BITNIC IBM-NETS List <IBM-NETS@BITNIC>
From:         UNIX-to-UNIX Copy <CMCL2!RUTGERS!SRI-SPAM!CSI!UUCP>
Subject:      uuxqt cmd (rmail ghere) status (signal 0, exit 67)
To:           Ross Patterson <A024012@RUTVM1>
 
 
------------------ End   of included file UUCP     MAIL        -----------------
    Please  note that  the Sender:  was  added by  LISTSERV, and  thus
couldn't trip test which path through  usenet the file took.  The only
tip off was the Subject:, and that required some knowledge of esoteric
bits of Unix to understand.  Remember, the first alarm was issued only
after the list had received several of these.
 
    So, how 'bout it?
 
Ross Patterson
Rutgers University