The day SORBS goes away ...

[randy at psg.com (Randy Bush)]

  drop    condition     = ${if isip4{$sender_host_address}}
          message       = blocked because $sender_host_address is \
                          in  blacklist at $dnslist_domain: $dnslist_text
          !dnslists     = list.dnswl.org
          dnslists      = dialups.mail-abuse.org \
                          : rbl-plus.mail-abuse.org \
                          : dnsbl.sorbs.net \
                          : zen.spamhaus.org
          logwrite      = REJECT because $sender_host_address listed in $dnslist_domain

works pretty well for me.  looking forward to a bit of ipv6 prophylaxis

randy