fallback to bounce.to, improve formatting, add bounce test

Author: NickOvt

plugins/core/email-bounce.js

@@ -3,17 +3,19 @@
 const os = require('os');
 const MimeNode = require('nodemailer/lib/mime-node');
 
+function formatRecipients(value) {
+    return []
+        .concat(value || [])
+        .map(entry => ((entry && entry.address) || entry || '').toString().trim())
+        .filter(entry => entry);
+}
+
 function getSingleRecipient(value) {
-    return (
-        []
-            .concat(value || [])
-            .map(entry => ((entry && entry.address) || entry || '').toString().trim())
-            .find(entry => entry) || ''
-    );
+    return formatRecipients(value).find(entry => entry) || '';
 }
 
 function getFailedRecipient(bounce) {
-    return getSingleRecipient(bounce.recipient || bounce.envelope?.to);
+    return getSingleRecipient(bounce.recipient || bounce.envelope?.to || bounce.to);
 }
 
 function getBounceSubject(bounce, isDelayed) {
@@ -41,7 +43,8 @@ module.exports.init = function (app, done) {
         let to = bounce.from;
         let sendingZone = cfg.sendingZone || app.config.sendingZone;
         let failedRecipient = getFailedRecipient(bounce);
-        let originalRecipientsText = `\nOriginal message recipients:\n    ${bounce.to}\n`;
+        let originalRecipients = formatRecipients(bounce.to);
+        let originalRecipientsText = originalRecipients.length ? `\nOriginal message recipients:\n    ${originalRecipients.join('\n    ')}\n` : '';
 
         let rootNode = new MimeNode('multipart/report; report-type=delivery-status');
 
@@ -51,7 +54,9 @@ module.exports.init = function (app, done) {
         rootNode.setHeader('From', fromAddress);
         rootNode.setHeader('To', to);
         rootNode.setHeader('X-Sending-Zone', sendingZone);
-        rootNode.setHeader('X-Failed-Recipients', bounce.to);
+        if (originalRecipients.length) {
+            rootNode.setHeader('X-Failed-Recipients', originalRecipients.join(', '));
+        }
         rootNode.setHeader('Auto-Submitted', 'auto-replied');
         rootNode.setHeader('Subject', getBounceSubject(bounce, isDelayed));
 

test/email-bounce-test.js

@@ -0,0 +1,94 @@
+'use strict';
+
+const emailBounce = require('../plugins/core/email-bounce');
+
+function createHeaders() {
+    return {
+        getFirst(key) {
+            if (key === 'Message-ID') {
+                return '<test-message@example.com>';
+            }
+            return '';
+        },
+        get(key) {
+            if (key === 'Received') {
+                return [];
+            }
+            return [];
+        },
+        build() {
+            return 'Message-ID: <test-message@example.com>\r\n';
+        }
+    };
+}
+
+function createApp() {
+    const hooks = new Map();
+    return {
+        hooks,
+        config: {
+            zoneConfig: {},
+            mailerDaemon: 'Mailer Daemon <mailer-daemon@[HOSTNAME]>',
+            sendingZone: 'default'
+        },
+        addHook(name, handler) {
+            hooks.set(name, handler);
+        },
+        getQueue() {
+            return {
+                generateId(callback) {
+                    callback(null, 'test-bounce-id');
+                }
+            };
+        },
+        logger: {
+            info() {},
+            error() {}
+        },
+        remotelog() {}
+    };
+}
+
+module.exports['Email bounce falls back to bounce.to for failed recipient'] = test => {
+    const app = createApp();
+    emailBounce.init(app, () => {});
+
+    const queueBounce = app.hooks.get('queue:bounce');
+
+    const bounce = {
+        id: 'message-id',
+        sessionId: 'session-id',
+        zone: 'default',
+        from: 'sender@example.com',
+        to: [{ address: 'failed@example.com' }],
+        seq: '001',
+        headers: createHeaders(),
+        name: 'mx.example.com',
+        arrivalDate: new Date('2026-03-25T10:00:00Z').toISOString(),
+        response: '550 5.1.1 No such user'
+    };
+
+    const maildrop = {
+        add(envelope, stream, callback) {
+            const chunks = [];
+            stream.on('data', chunk => chunks.push(chunk));
+            stream.on('error', callback);
+            stream.on('end', () => {
+                const message = Buffer.concat(chunks).toString();
+
+                test.equal(envelope.to, 'sender@example.com');
+                test.ok(/Subject: Delivery Status Notification \(Failure: failed@example\.com\)/.test(message));
+                test.ok(/Final-Recipient: rfc822; failed@example\.com/.test(message));
+                test.ok(/X-Failed-Recipients: failed@example\.com/.test(message));
+                test.ok(/Original message recipients:\s+failed@example\.com/.test(message));
+
+                callback();
+            });
+        }
+    };
+
+    queueBounce(bounce, maildrop, err => {
+        test.ifError(err);
+        test.done();
+    });
+};