Builting ZoneMTA with the plugins

zone-mta/plugins/mailtrain-main.js

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+'use strict';
+
+// Set module title
+module.exports.title = 'Mailtrain integration (main)';
+
+// Initialize the module
+module.exports.init = (app, done) => {
+
+    process.send({
+        type: 'zone-mta-started'
+    });
+
+    done();
+};

zone-mta/plugins/mailtrain-receiver.js

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+'use strict';
+
+// Set module title
+module.exports.title = 'Mailtrain integration (receiver)';
+
+// Initialize the module
+module.exports.init = (app, done) => {
+
+    app.addHook('message:headers', (envelope, messageInfo, next) => {
+        const headers = envelope.headers;
+
+        if (!envelope.dkim.keys) {
+            envelope.dkim.keys = [];
+        }
+
+        const dkimHeaderValue = headers.getFirst('x-mailtrain-dkim');
+
+        if (dkimHeaderValue) {
+            const dkimKey = JSON.parse(dkimHeaderValue);
+
+            envelope.dkim.keys.push(dkimKey);
+
+            headers.remove('x-mailtrain-dkim');
+        }
+
+        return next();
+    });
+
+    app.addHook('smtp:auth', (auth, session, next) => {
+        if (auth.username === app.config.username && auth.password === app.config.password) {
+            next();
+        } else {
+            // do not provide any details about the failure
+            const err = new Error('Authentication failed');
+            err.responseCode = 535;
+            return next(err);
+        }
+    });
+
+    // all set up regarding this plugin
+    done();
+};