You might test if your server is able to communicate with SFS by setting the option to disabled then trying to register with a spammer address. I just tried
bestmymail2010@gmail.com on our forums and it was blocked.
2010-10-21 16:27:20 xx.xx.xx.xx yutryutryutrutrtr
bestmymail2010@gmail.com Spam-O-Matic Tagged email -
bestmymail2010@gmail.com - Spammer Found and rejected.