fix(tests): update tests and test helpers to current email/DNS APIs, use non-privileged ports, and improve robustness and resilience

test/helpers/smtp.client.ts

@@ -16,11 +16,13 @@ export function createTestSmtpClient(options: Partial<ISmtpClientOptions> = {}):
     maxConnections: options.maxConnections || 5,
     maxMessages: options.maxMessages || 100,
     debug: options.debug || false,
+    pool: options.pool || false,  // Enable connection pooling
+    domain: options.domain,        // Client domain for EHLO
     tls: options.tls || {
       rejectUnauthorized: false
     }
   };
-  
+
   return smtpClientMod.createSmtpClient(defaultOptions);
 }