Add experimental watchdog

data/conf/rspamd/local.d/metrics.conf

@@ -17,3 +17,20 @@ group "bayes" {
 		description = "Message probably ham, probability: ";
 	}
 }
+group "MX" {
+	symbol "MX_INVALID" {
+	  score = 0.5;
+	  description = "No connectable MX";
+	  one_shot = "true";
+	}
+	symbol "MX_MISSING" {
+	  score = 2.0;
+	  description = "No MX record";
+	  one_shot = "true";
+	}
+	symbol "MX_GOOD" {
+	  score = -0.01;
+	  description = "MX was ok";
+	  one_shot = "true";
+	}
+}