Bill Verity at "LISTSERV site administrators' forum" 
<[log in to unmask]> wrote on 09/13/2006 03:26:14 PM:

> We plan to run Spamassasin on our listserv machine to identify spam 
> as soon as we have a faster machine.  Question is what to do with it 
> after it is identified.   Our thought is to simply reject any mail 
> that scores "high" from spamassassin.  The value of high is yet to be 
> determined.   This may make spamcop at little happier, but probably 
> not enough to keep us off their list.

Define "reject."  Return it to the alleged sender?  Are you going to 
discard the message?  Return a permanent SMTP error code?

The last is only possible if you score it while the SMTP connection is 
open.  The spam filter (based on a sendmail's milter API) I use does the 
third option.  The first option will get you blacklisted for backscatter 
spam.  The second choice is the best bet if you can't use #3, but false 
positives will get lost.