REDDOXX recommends the following Realtime Blacklist filter beside the already default list bl.spamcop.net.
Please Keep in mind, that the RBL Filter is not maintained by REDDOXX and only selected from a list of common RBL Filters.
ix.dnsbl.manitu.net
bb.barracudacentral.org
If however, still spam attacks are not filtered by the above lists, check http://mxtoolbox.com for RBL Filter lists, that would block the sender and add the RBL Filter to the REDDOXX Appliance.
More Information can be found in the administration manual