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/composites.conf

@@ -34,3 +34,6 @@ FORGED_W_BAD_POLICY {
   expression = "( ~g+:policies | ~R_SPF_NA) & ( ~FROM_NEQ_ENVFROM & ~FORGED_SENDER )"
   score = 3.0;
 }
+RBL_EXCLUDE_FWD_HOST {
+  expression = "-WHITELISTED_FWD_HOST & ^g:rbl"
+}