feat(email): add persistent smartmta storage and runtime-managed email domain syncing

test/test.dcrouter.email.ts

@@ -143,6 +143,9 @@ tap.test('DcRouter class - Email config with domains and routes', async () => {
 
   // Verify unified email server was initialized
   expect(router.emailServer).toBeTruthy();
+  expect((router.emailServer as any).options.hostname).toEqual('mail.example.com');
+  expect((router.emailServer as any).options.persistRoutes).toEqual(false);
+  expect((router.emailServer as any).options.queue.storageType).toEqual('disk');
 
   // Stop the router
   await router.stop();