--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mod_register_dnsbl/mod_register_dnsbl.lua	Thu Mar 17 12:11:12 2016 +0000
@@ -0,0 +1,25 @@
+local adns = require "net.adns";
+local rbl = module:get_option_string("registration_rbl");
+
+local function reverse(ip, suffix)
+	local a,b,c,d = ip:match("^(%d+%).(%d+%).(%d+%).(%d+%)$");
+	if not a then return end
+	return ("%d.%d.%d.%d.%s"):format(d,c,b,a, suffix);
+end
+
+-- TODO async
+-- module:hook("user-registering", function (event) end);
+
+module:hook("user-registered", function (event)
+	local session = event.session;
+	local ip = session and session.ip;
+	local rbl_ip = ip and reverse(ip, rbl);
+	if rbl_ip then
+		local log = session.log;
+		adns.lookup(function (reply)
+			if reply and reply[1] then
+				log("warn", "Registration from IP %s found in RBL", ip);
+			end
+		end, rbl_ip);
+	end
+end);