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_reliability/test.crel-07.resource-cleanup.ts

@@ -0,0 +1,52 @@
+import { tap, expect } from '@git.zone/tstest/tapbundle';
+import { createTestServer } from '../../helpers/server.loader.ts';
+import { createTestSmtpClient } from '../../helpers/smtp.client.ts';
+
+tap.test('CREL-07: Resource Cleanup Tests', async () => {
+  console.log('\n🧹 Testing SMTP Client Resource Cleanup');
+  console.log('=' .repeat(60));
+
+  const testServer = await createTestServer({});
+
+  try {
+    console.log('\nTest 1: Basic client creation and cleanup');
+    
+    // Create a client
+    const smtpClient = createTestSmtpClient({
+      host: testServer.hostname,
+      port: testServer.port
+    });
+    console.log('  ✓ Client created');
+
+    // Verify connection
+    try {
+      const verifyResult = await smtpClient.verify();
+      console.log('  ✓ Connection verified:', verifyResult);
+    } catch (error) {
+      console.log('  ⚠️ Verify failed:', error.message);
+    }
+
+    // Close the client
+    smtpClient.close();
+    console.log('  ✓ Client closed');
+
+    console.log('\nTest 2: Multiple close calls');
+    const testClient = createTestSmtpClient({
+      host: testServer.hostname,
+      port: testServer.port
+    });
+
+    // Close multiple times - should not throw
+    testClient.close();
+    testClient.close();
+    testClient.close();
+    console.log('  ✓ Multiple close calls handled safely');
+
+    console.log('\n✅ CREL-07: Resource cleanup tests completed');
+
+  } finally {
+    testServer.server.close();
+  }
+});
+
+tap.start();