[Conf] Add MSBL proposed return codes

conf/modules.d/emails.conf

             dnsbl = "email.rspamd.com";
             check_replyto = true;
             hash = "blake2";
+            returncodes = {
+              RSPAMD_EMAILBL = "127.0.0.2";
+            }
         }
         MSBL_EBL {
             dnsbl = "ebl.msbl.org";
             domain_only = false;
             check_replyto = true;
             hash = "sha1";
-            expect_ip = "127.0.0.2";
+            returncodes = {
+              MSBL_EBL = [
+                "127.0.0.2",
+                "127.0.0.3"
+              ];
+              MSBL_EBL_GREY = [
+                "127.0.1.2",
+                "127.0.1.3"
+              ];
+            }
         }
     }
     .include(try=true,priority=5) "${DBDIR}/dynamic/emails.conf"

conf/scores.d/surbl_group.conf

         one_shot = true;
     }
 
+    "MSBL_EBL_GREY" {
+        weight = 0.5; # TODO: test it
+        description = "MSBL emailbl grey list";
+        one_shot = true;
+    }
+
     "SEM_URIBL_UNKNOWN" {
         weight = 0.0;
         description = "Spameatingmonkey uribl: unknown result";