feat(storage): add comprehensive tests for StorageManager with memory, filesystem, and custom function backends

feat(email): implement EmailSendJob class for robust email delivery with retry logic and MX record resolution

feat(mail): restructure mail module exports for simplified access to core and delivery functionalities

test/suite/smtpclient_performance/test.cperf-08.dns-caching.ts

@@ -0,0 +1,50 @@
+import { tap, expect } from '@git.zone/tstest/tapbundle';
+import { createTestServer } from '../../helpers/server.loader.ts';
+import { createTestSmtpClient } from '../../helpers/smtp.client.ts';
+import { Email } from '../../../ts/mail/core/classes.email.ts';
+
+tap.test('CPERF-08: DNS Caching Tests', async () => {
+  console.log('\n🌐 Testing SMTP Client DNS Caching');
+  console.log('=' .repeat(60));
+
+  const testServer = await createTestServer({});
+
+  try {
+    console.log('\nTest: DNS caching with multiple connections');
+    
+    // Create multiple clients to test DNS caching
+    const clients = [];
+    
+    for (let i = 0; i < 3; i++) {
+      const smtpClient = createTestSmtpClient({
+        host: testServer.hostname,
+        port: testServer.port
+      });
+      clients.push(smtpClient);
+      console.log(`  ✓ Client ${i + 1} created (DNS should be cached)`);
+    }
+
+    // Send email with first client
+    const email = new Email({
+      from: 'sender@example.com',
+      to: 'recipient@example.com',
+      subject: 'DNS Caching Test',
+      text: 'Testing DNS caching efficiency'
+    });
+
+    const result = await clients[0].sendMail(email);
+    console.log('  ✓ Email sent successfully');
+    expect(result).toBeDefined();
+
+    // Clean up all clients
+    clients.forEach(client => client.close());
+    console.log('  ✓ All clients closed');
+
+    console.log('\n✅ CPERF-08: DNS caching tests completed');
+
+  } finally {
+    testServer.server.close();
+  }
+});
+
+tap.start();