check for local_mx only when default route is used (#3307)

It only checks local mx if it falls through to the DNS looked up route - so
any plugin's mx is excluded.

---------

Co-authored-by: SH <sh@analogic.cz>
Co-authored-by: Matt Simerson <matt@tnpi.net>

Changes.md

@@ -3,6 +3,7 @@
 
 #### Changed
 
+- check for local_mx only when default route is used #3307
 - test: add a connection.response test case with DSN #3305
 - deps: bump all versions to latest #3303
 - auth_base: enable disabling constrain_sender at runtime #3298

outbound/hmail.js

@@ -228,8 +228,10 @@ class HMailItem extends events.EventEmitter {
 
         // if none of the above return codes, drop through to this...
         mx_lookup.lookup_mx(this.todo.domain, (err, mxs) => {
-            this.found_mx(err, mxs);
-        });
+            if (mxs) mxs.forEach(m => { m.from_dns = true; });
+
+            this.found_mx (err, mxs)
+        })
     }
 
     found_mx (err, mxs) {
@@ -272,15 +274,11 @@ class HMailItem extends events.EventEmitter {
                 if (mxlist[mx].path) {
                     this.mxlist.push(mxlist[mx]);
                 }
-                else if (obc.cfg.ipv6_enabled) {
-                    this.mxlist.push(
-                        { exchange: mxlist[mx].exchange, priority: mxlist[mx].priority, port: mxlist[mx].port, using_lmtp: mxlist[mx].using_lmtp, family: 'AAAA' },
-                        { exchange: mxlist[mx].exchange, priority: mxlist[mx].priority, port: mxlist[mx].port, using_lmtp: mxlist[mx].using_lmtp, family: 'A' }
-                    );
-                }
                 else {
-                    mxlist[mx].family = 'A';
-                    this.mxlist.push(mxlist[mx]);
+                    if (obc.cfg.ipv6_enabled) {
+                        this.mxlist.push(Object.assign({}, mxlist[mx], { family: 'AAAA' }));
+                    }
+                    this.mxlist.push(Object.assign({}, mxlist[mx], { family: 'A' }));
                 }
             }
             this.try_deliver();
@@ -300,11 +298,9 @@ class HMailItem extends events.EventEmitter {
         const mx = this.mxlist.shift();
         const host = mx.exchange;
 
-        if (!obc.cfg.local_mx_ok) {
-            if (await net_utils.is_local_host(host)) {
-                this.loginfo(`MX ${host} is local, skipping since local_mx_ok=false`)
-                return this.try_deliver(); // try next MX
-            }
+        if (!obc.cfg.local_mx_ok && mx.from_dns && await net_utils.is_local_host(host)) {
+            this.loginfo(`MX ${host} is local, skipping since local_mx_ok=false`)
+            return this.try_deliver(); // try next MX
         }
 
         this.force_tls = this.todo.force_tls;
@@ -371,7 +367,7 @@ class HMailItem extends events.EventEmitter {
             host = mx.path;
         }
 
-        this.logdebug(`delivering from: ${mx.bind_helo} to: ${host}:${port}${mx.using_lmtp ? " using LMTP" : ""} (${delivery_queue.length()}) (${temp_fail_queue.length()})`)
+        this.logdebug(`delivering from: ${mx.bind_helo} to: ${host}:${port}${mx.using_lmtp ? " using LMTP" : ""}${mx.from_dns ? " (via DNS)" : ""} (${delivery_queue.length()}) (${temp_fail_queue.length()})`)
         client_pool.get_client(port, host, mx.bind, !!mx.path, (err, socket) => {
             if (err) {
                 if (/connection timed out|connect ECONNREFUSED/.test(err)) {
@@ -729,7 +725,7 @@ class HMailItem extends events.EventEmitter {
                             // The response is our challenge
                             return send_command(cram_md5_response(mx.auth_user, mx.auth_pass, resp));
                         default:
-                            // This shouldn't happen...
+                        // This shouldn't happen...
                     }
                 }
                 // Error