> Apart from that we plan to put a dedicated spam/virus filter in front of
> our listserv-boxes to minimise the backscatter. Basically the filter-box
> would prevent obvious spam and virus-infected mails to even reach the
> listserv-boxes and thus would also prevent much of the annoyances caused
> by both backscatter and spam-related messages to our list-owners that
> are not and can not be filtered by the standard anti-spam/virus tools of
> listserv itself.

This will help of course, but unfortunately no spam filter is 100% accurate,
so you will only reduce the frequency of blacklisting, not eliminate the
problem. The only solution is for the anti-spam community to accept that
spammers have outsmarted "secret" mailboxes by using harvested addresses as
the message origin.

  Eric