Reduce Rspamd DNSBL false positives (#3311)

* rspamd: ignore Spamhaus XBL for Received headers

* rspamd: ignore SORBS RBL for forwarding hosts

* rspamd: ignore RBLs for forwarding hosts

data/conf/rspamd/local.d/rbl_group.conf

@@ -45,4 +45,8 @@ symbols = {
     score = 2.0;  
     description = "List of networks hijacked from their original owners, some of which have already used for spamming.";  
   }
+  "RECEIVED_SPAMHAUS_XBL" {
+    weight = 0.0;
+    description = "Received address is listed in ZEN XBL";
+  }
 }