If I understand the problem correctly, ...

All of our incoming (and outgoing) Listserv mail hits our enterprise 
virus and junk/spam scanners first.  The scanners "mark" the spam, 
making it easy to have a Listserv CONTENT_FILTER (for the site) 
eliminate them from all processing.  Older versions of Listserv may not 
have CONTENT_FILTER.

cheers, wayne

Rodriguez, Pedro wrote, in part,  on 12/12/2005 12:02 PM:
> I keep getting junk mail in my listserv from automatically generated
> e-mail accounts that do not exist.  How can I prevent those to come
> through this listserv?
>