I've been really impressed with messagewall its very effective and seems to be very low on resource.
if anyone is interested in using messagewall please ready the info below
you can dl Craig Fosters Beta from here:
http://mirror.contribs.org/smeserver/contribs/cfoster/beta/messagewall/there are a couple of little things that need to be changed, contact me if you need any help.
Anyway
I've been talking to one of the tech people at dsbl (the main spammers DB that MW uses) Fred pointed out a couple of things about message wall. One was just an intersting fact, that one of the co-founders of dsbl co-wrote messagewall.
the other was the that because the last stable version of message wall was written over a year ago(if it works well don't fix it I say

there are a couple of dsbl server names in the profiles files that no longer exist
these lines are
dnsdcc=1,aa.dcc.dsbl.org
dnsdcc=1,ba.dcc.dsbl.org
you will find this in the hight level profiles (Extreme...etc)
I would also look at removing all dnsbl entries in these files others other than
dnsbl=1,list.dsbl.org
dnsbl=1,multihop.dsbl.org
and also add in
dnsbl=1,relays.ordb.org
Any others and you might start running in to the problem of it not using the blacklists at all.
I'm also looking at writing a web interface to make it a little easier to configure, any suggestions on areas you would like to configure please let me know.
If I come across anything else that might be of interest I'll keep everyone posted.