fix(mail2http): retry 5xx responses

Author: andris9

lib/sender.js

@@ -686,7 +686,16 @@ class Sender extends EventEmitter {
     handleResponseError(delivery, connection, err, callback) {
         let bounce;
 
-        if (!err.responseCode && !/^\d{3}\b/.test(err.response || err.message)) {
+        if (err.protocol === 'http') {
+            // mail2http failures
+            bounce = {
+                action: err.httpResponse >= 400 && err.httpResponse < 500 ? 'reject' : 'defer',
+                category: 'http',
+                message: err.response || err.message,
+                code: err.httpResponse || 488,
+                status: false
+            };
+        } else if (!err.responseCode && !/^\d{3}\b/.test(err.response || err.message)) {
             // timeouts, node network errors etc.
             bounce = {
                 action: 'defer',