Is this not the same as the new "spoofed subscription" feature of 1.8c?
(See excerpt below)

On Fri, 21 Feb 1997 15:24:08 CST Chris Barnes said:
>What is wanted:
>   Listserv has implemented and "anti-spam" feature in which the server
>   looks for the same message which is sent to multiple lists.  I would
>   like to see the same type of checking implemented when an address
>   is subscribed to multiple lists within a set amuont of time.

Excerpt from the maintainer's release notes:

Starting  with  version  1.8c,  LISTSERV  is now  able  to  detect  these
"spoofed"  subscription   attacks  automatically.   When  more   than  50
subscription requests are received from the  same account in a short time
frame, LISTSERV  automatically undoes  all the subscription  requests and
rejects any  further subscription attempt  for a certain period  of time.
This applies even  to requests that LISTSERV forwarded  to other servers;
LISTSERV will  then send a SIGNOFF  request to the remote  server for the
address in question.  Note that, in some cases, the  subscription may not
be undone,  either because  of a temporary  condition (locked  list, etc)
preventing  LISTSERV from  deleting the  user,  or because  the list  was
configured with "Subscription= By owner" and the owner manually added the
victim after the arrival of the undo request.