update

test/suite/smtpserver_reliability/test.rel-01.long-running-operation.ts

@@ -0,0 +1,344 @@
+import * as plugins from '@git.zone/tstest/tapbundle';
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as net from 'net';
+import { startTestServer, stopTestServer } from '../../helpers/server.loader.js';
+
+const TEST_PORT = 2525;
+
+let testServer;
+
+tap.test('prepare server', async () => {
+  testServer = await startTestServer({ port: TEST_PORT });
+  await new Promise(resolve => setTimeout(resolve, 100));
+});
+
+tap.test('REL-01: Long-running operation - Continuous email sending', async (tools) => {
+  const done = tools.defer();
+  const testDuration = 30000; // 30 seconds
+  const operationInterval = 2000; // 2 seconds between operations
+  const startTime = Date.now();
+  const endTime = startTime + testDuration;
+  
+  let operations = 0;
+  let successful = 0;
+  let errors = 0;
+  let connectionIssues = 0;
+  const operationResults: Array<{
+    operation: number;
+    success: boolean;
+    duration: number;
+    error?: string;
+    timestamp: number;
+  }> = [];
+
+  console.log(`Running long-duration test for ${testDuration/1000} seconds...`);
+
+  const performOperation = async (operationId: number): Promise<void> => {
+    const operationStart = Date.now();
+    operations++;
+
+    try {
+      const socket = net.createConnection({
+        host: 'localhost',
+        port: TEST_PORT,
+        timeout: 10000
+      });
+
+      const result = await new Promise<{ success: boolean; error?: string; connectionIssue?: boolean }>((resolve) => {
+        let step = 'connecting';
+        let receivedData = '';
+
+        const timeout = setTimeout(() => {
+          socket.destroy();
+          resolve({
+            success: false,
+            error: `Timeout in step ${step}`,
+            connectionIssue: true
+          });
+        }, 10000);
+
+        socket.on('connect', () => {
+          step = 'connected';
+        });
+
+        socket.on('data', (chunk) => {
+          receivedData += chunk.toString();
+          const lines = receivedData.split('\r\n');
+
+          for (const line of lines) {
+            if (!line.trim()) continue;
+
+            // Check for errors
+            if (line.match(/^[45]\d\d\s/)) {
+              clearTimeout(timeout);
+              socket.destroy();
+              resolve({
+                success: false,
+                error: `SMTP error in ${step}: ${line}`,
+                connectionIssue: false
+              });
+              return;
+            }
+
+            // Process responses
+            if (step === 'connected' && line.startsWith('220')) {
+              step = 'ehlo';
+              socket.write(`EHLO longrun-${operationId}\r\n`);
+            } else if (step === 'ehlo' && line.includes('250 ') && !line.includes('250-')) {
+              step = 'mail_from';
+              socket.write(`MAIL FROM:<sender${operationId}@example.com>\r\n`);
+            } else if (step === 'mail_from' && line.startsWith('250')) {
+              step = 'rcpt_to';
+              socket.write(`RCPT TO:<recipient${operationId}@example.com>\r\n`);
+            } else if (step === 'rcpt_to' && line.startsWith('250')) {
+              step = 'data';
+              socket.write('DATA\r\n');
+            } else if (step === 'data' && line.startsWith('354')) {
+              step = 'email_content';
+              const emailContent = [
+                `From: sender${operationId}@example.com`,
+                `To: recipient${operationId}@example.com`,
+                `Subject: Long Running Test Operation ${operationId}`,
+                `Date: ${new Date().toUTCString()}`,
+                '',
+                `This is test operation ${operationId} for long-running reliability testing.`,
+                `Timestamp: ${Date.now()}`,
+                '.',
+                ''
+              ].join('\r\n');
+              socket.write(emailContent);
+            } else if (step === 'email_content' && line.startsWith('250')) {
+              step = 'quit';
+              socket.write('QUIT\r\n');
+            } else if (step === 'quit' && line.startsWith('221')) {
+              clearTimeout(timeout);
+              socket.end();
+              resolve({
+                success: true
+              });
+              return;
+            }
+          }
+        });
+
+        socket.on('error', (error) => {
+          clearTimeout(timeout);
+          resolve({
+            success: false,
+            error: error.message,
+            connectionIssue: true
+          });
+        });
+
+        socket.on('close', () => {
+          if (step !== 'quit') {
+            clearTimeout(timeout);
+            resolve({
+              success: false,
+              error: 'Connection closed unexpectedly',
+              connectionIssue: true
+            });
+          }
+        });
+      });
+
+      const duration = Date.now() - operationStart;
+
+      if (result.success) {
+        successful++;
+      } else {
+        errors++;
+        if (result.connectionIssue) {
+          connectionIssues++;
+        }
+      }
+
+      operationResults.push({
+        operation: operationId,
+        success: result.success,
+        duration,
+        error: result.error,
+        timestamp: operationStart
+      });
+
+    } catch (error) {
+      errors++;
+      operationResults.push({
+        operation: operationId,
+        success: false,
+        duration: Date.now() - operationStart,
+        error: error instanceof Error ? error.message : 'Unknown error',
+        timestamp: operationStart
+      });
+    }
+  };
+
+  try {
+    // Run operations continuously until end time
+    while (Date.now() < endTime) {
+      const operationStart = Date.now();
+      
+      await performOperation(operations + 1);
+
+      // Calculate wait time for next operation
+      const nextOperation = operationStart + operationInterval;
+      const waitTime = nextOperation - Date.now();
+
+      if (waitTime > 0 && Date.now() < endTime) {
+        await new Promise(resolve => setTimeout(resolve, waitTime));
+      }
+
+      // Progress update every 5 operations
+      if (operations % 5 === 0) {
+        console.log(`Progress: ${operations} operations, ${successful} successful, ${errors} errors`);
+      }
+    }
+
+    // Calculate results
+    const totalDuration = Date.now() - startTime;
+    const successRate = successful / operations;
+    const connectionIssueRate = connectionIssues / operations;
+    const avgOperationTime = operationResults.reduce((sum, r) => sum + r.duration, 0) / operations;
+
+    console.log(`\nLong-Running Operation Results:`);
+    console.log(`Total duration: ${(totalDuration/1000).toFixed(1)}s`);
+    console.log(`Total operations: ${operations}`);
+    console.log(`Successful: ${successful} (${(successRate * 100).toFixed(1)}%)`);
+    console.log(`Errors: ${errors}`);
+    console.log(`Connection issues: ${connectionIssues} (${(connectionIssueRate * 100).toFixed(1)}%)`);
+    console.log(`Average operation time: ${avgOperationTime.toFixed(0)}ms`);
+
+    // Show last few operations for debugging
+    console.log('\nLast 5 operations:');
+    operationResults.slice(-5).forEach(op => {
+      console.log(`  Op ${op.operation}: ${op.success ? 'success' : 'failed'} (${op.duration}ms)${op.error ? ' - ' + op.error : ''}`);
+    });
+
+    // Test passes with 85% success rate and max 10% connection issues
+    expect(successRate).toBeGreaterThanOrEqual(0.85);
+    expect(connectionIssueRate).toBeLessThanOrEqual(0.1);
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-01: Long-running operation - Server stability check', async (tools) => {
+  const done = tools.defer();
+  const checkDuration = 15000; // 15 seconds
+  const checkInterval = 3000; // 3 seconds between checks
+  const startTime = Date.now();
+  const endTime = startTime + checkDuration;
+  
+  const stabilityChecks: Array<{
+    timestamp: number;
+    responseTime: number;
+    success: boolean;
+    error?: string;
+  }> = [];
+
+  console.log(`\nRunning server stability checks for ${checkDuration/1000} seconds...`);
+
+  try {
+    while (Date.now() < endTime) {
+      const checkStart = Date.now();
+      
+      const socket = net.createConnection({
+        host: 'localhost',
+        port: TEST_PORT,
+        timeout: 5000
+      });
+
+      const checkResult = await new Promise<{ success: boolean; responseTime: number; error?: string }>((resolve) => {
+        const connectTime = Date.now();
+        let greetingReceived = false;
+
+        const timeout = setTimeout(() => {
+          socket.destroy();
+          resolve({
+            success: false,
+            responseTime: Date.now() - connectTime,
+            error: 'Timeout waiting for greeting'
+          });
+        }, 5000);
+
+        socket.on('connect', () => {
+          // Connected
+        });
+
+        socket.once('data', (chunk) => {
+          const response = chunk.toString();
+          clearTimeout(timeout);
+          greetingReceived = true;
+          
+          if (response.startsWith('220')) {
+            socket.write('QUIT\r\n');
+            socket.end();
+            resolve({
+              success: true,
+              responseTime: Date.now() - connectTime
+            });
+          } else {
+            socket.end();
+            resolve({
+              success: false,
+              responseTime: Date.now() - connectTime,
+              error: `Unexpected greeting: ${response.substring(0, 50)}`
+            });
+          }
+        });
+
+        socket.on('error', (error) => {
+          clearTimeout(timeout);
+          resolve({
+            success: false,
+            responseTime: Date.now() - connectTime,
+            error: error.message
+          });
+        });
+      });
+
+      stabilityChecks.push({
+        timestamp: checkStart,
+        responseTime: checkResult.responseTime,
+        success: checkResult.success,
+        error: checkResult.error
+      });
+
+      console.log(`Stability check ${stabilityChecks.length}: ${checkResult.success ? 'OK' : 'FAILED'} (${checkResult.responseTime}ms)`);
+
+      // Wait for next check
+      const nextCheck = checkStart + checkInterval;
+      const waitTime = nextCheck - Date.now();
+      if (waitTime > 0 && Date.now() < endTime) {
+        await new Promise(resolve => setTimeout(resolve, waitTime));
+      }
+    }
+
+    // Analyze stability
+    const successfulChecks = stabilityChecks.filter(c => c.success).length;
+    const avgResponseTime = stabilityChecks
+      .filter(c => c.success)
+      .reduce((sum, c) => sum + c.responseTime, 0) / successfulChecks || 0;
+    const maxResponseTime = Math.max(...stabilityChecks.filter(c => c.success).map(c => c.responseTime));
+
+    console.log(`\nStability Check Results:`);
+    console.log(`Total checks: ${stabilityChecks.length}`);
+    console.log(`Successful: ${successfulChecks} (${(successfulChecks/stabilityChecks.length * 100).toFixed(1)}%)`);
+    console.log(`Average response time: ${avgResponseTime.toFixed(0)}ms`);
+    console.log(`Max response time: ${maxResponseTime}ms`);
+
+    // All checks should succeed for stable server
+    expect(successfulChecks).toEqual(stabilityChecks.length);
+    expect(avgResponseTime).toBeLessThan(1000);
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('cleanup server', async () => {
+  await stopTestServer(testServer);
+});
+
+tap.start();

test/suite/smtpserver_reliability/test.rel-02.restart-recovery.ts

@@ -0,0 +1,328 @@
+import * as plugins from '@git.zone/tstest/tapbundle';
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as net from 'net';
+import { startTestServer, stopTestServer } from '../../helpers/server.loader.js';
+
+const TEST_PORT = 2525;
+
+let testServer;
+
+// Helper function to wait for SMTP response
+const waitForResponse = (socket: net.Socket, expectedCode?: string, timeout = 5000): Promise<string> => {
+  return new Promise((resolve, reject) => {
+    let buffer = '';
+    const timer = setTimeout(() => {
+      socket.removeListener('data', handler);
+      reject(new Error(`Timeout waiting for ${expectedCode || 'any'} response`));
+    }, timeout);
+    
+    const handler = (data: Buffer) => {
+      buffer += data.toString();
+      const lines = buffer.split('\r\n');
+      
+      // Check if we have a complete response
+      for (const line of lines) {
+        if (expectedCode) {
+          if (line.startsWith(expectedCode + ' ')) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        } else {
+          // Any complete response line
+          if (line.match(/^\d{3} /)) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        }
+      }
+    };
+    
+    socket.on('data', handler);
+  });
+};
+
+tap.test('prepare server', async () => {
+  testServer = await startTestServer({ port: TEST_PORT });
+  await new Promise(resolve => setTimeout(resolve, 100));
+});
+
+tap.test('REL-02: Restart recovery - Server state after restart', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('Testing server state and recovery capabilities...');
+
+    // First, establish that server is working normally
+    const socket1 = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket1.once('connect', resolve);
+      socket1.once('error', reject);
+    });
+
+    // Read greeting
+    const greeting1 = await waitForResponse(socket1, '220');
+    expect(greeting1).toInclude('220');
+    console.log('Initial connection successful');
+
+    // Send EHLO
+    socket1.write('EHLO testhost\r\n');
+    await waitForResponse(socket1, '250');
+
+    // Complete a transaction
+    socket1.write('MAIL FROM:<sender@example.com>\r\n');
+    const mailResp1 = await waitForResponse(socket1, '250');
+    expect(mailResp1).toInclude('250');
+
+    socket1.write('RCPT TO:<recipient@example.com>\r\n');
+    const rcptResp1 = await waitForResponse(socket1, '250');
+    expect(rcptResp1).toInclude('250');
+
+    socket1.write('DATA\r\n');
+    const dataResp1 = await waitForResponse(socket1, '354');
+    expect(dataResp1).toInclude('354');
+
+    const emailContent = [
+      'From: sender@example.com',
+      'To: recipient@example.com',
+      'Subject: Pre-restart test',
+      '',
+      'Testing server state before restart.',
+      '.',
+      ''
+    ].join('\r\n');
+
+    socket1.write(emailContent);
+    const sendResp1 = await waitForResponse(socket1, '250');
+    expect(sendResp1).toInclude('250');
+
+    socket1.write('QUIT\r\n');
+    await waitForResponse(socket1, '221');
+    socket1.end();
+
+    console.log('Pre-restart transaction completed successfully');
+
+    // Simulate server restart by closing and reopening connections
+    console.log('\nSimulating server restart scenario...');
+    
+    // Wait a moment to simulate restart time
+    await new Promise(resolve => setTimeout(resolve, 2000));
+
+    // Test recovery after simulated restart
+    const socket2 = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket2.once('connect', resolve);
+      socket2.once('error', reject);
+    });
+
+    // Read greeting after "restart"
+    const greeting2 = await new Promise<string>((resolve) => {
+      socket2.once('data', (chunk) => {
+        resolve(chunk.toString());
+      });
+    });
+
+    expect(greeting2).toInclude('220');
+    console.log('Post-restart connection successful');
+
+    // Verify server is fully functional after restart
+    socket2.write('EHLO testhost-postrestart\r\n');
+    await waitForResponse(socket2, '250');
+
+    // Complete another transaction to verify full recovery
+    socket2.write('MAIL FROM:<sender2@example.com>\r\n');
+    const mailResp2 = await waitForResponse(socket2, '250');
+    expect(mailResp2).toInclude('250');
+
+    socket2.write('RCPT TO:<recipient2@example.com>\r\n');
+    const rcptResp2 = await waitForResponse(socket2, '250');
+    expect(rcptResp2).toInclude('250');
+
+    socket2.write('DATA\r\n');
+    const dataResp2 = await waitForResponse(socket2, '354');
+    expect(dataResp2).toInclude('354');
+
+    const postRestartEmail = [
+      'From: sender2@example.com',
+      'To: recipient2@example.com',
+      'Subject: Post-restart recovery test',
+      '',
+      'Testing server recovery after restart.',
+      '.',
+      ''
+    ].join('\r\n');
+
+    socket2.write(postRestartEmail);
+    const sendResp2 = await waitForResponse(socket2, '250');
+    expect(sendResp2).toInclude('250');
+
+    socket2.write('QUIT\r\n');
+    await waitForResponse(socket2, '221');
+    socket2.end();
+
+    console.log('Post-restart transaction completed successfully');
+    console.log('Server recovered successfully from restart');
+
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-02: Restart recovery - Multiple rapid reconnections', async (tools) => {
+  const done = tools.defer();
+  const rapidConnections = 10;
+  let successfulReconnects = 0;
+
+  try {
+    console.log(`\nTesting rapid reconnection after disruption (${rapidConnections} attempts)...`);
+
+    for (let i = 0; i < rapidConnections; i++) {
+      try {
+        const socket = net.createConnection({
+          host: 'localhost',
+          port: TEST_PORT,
+          timeout: 5000
+        });
+
+        await new Promise<void>((resolve, reject) => {
+          const timeout = setTimeout(() => {
+            socket.destroy();
+            reject(new Error('Connection timeout'));
+          }, 5000);
+
+          socket.once('connect', () => {
+            clearTimeout(timeout);
+            resolve();
+          });
+          socket.once('error', (err) => {
+            clearTimeout(timeout);
+            reject(err);
+          });
+        });
+
+        // Read greeting
+        try {
+          const greeting = await waitForResponse(socket, '220', 3000);
+          if (greeting.includes('220')) {
+            successfulReconnects++;
+            socket.write('QUIT\r\n');
+            await waitForResponse(socket, '221', 1000).catch(() => {});
+            socket.end();
+          } else {
+            socket.destroy();
+          }
+        } catch (error) {
+          socket.destroy();
+          throw error;
+        }
+
+        // Very short delay between attempts
+        await new Promise(resolve => setTimeout(resolve, 100));
+
+      } catch (error) {
+        console.log(`Reconnection ${i + 1} failed:`, error.message);
+      }
+    }
+
+    const reconnectRate = successfulReconnects / rapidConnections;
+    console.log(`Successful reconnections: ${successfulReconnects}/${rapidConnections} (${(reconnectRate * 100).toFixed(1)}%)`);
+
+    // Expect high success rate for good recovery
+    expect(reconnectRate).toBeGreaterThanOrEqual(0.8);
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-02: Restart recovery - State persistence check', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting server state persistence across connections...');
+
+    // Create initial connection and start transaction
+    const socket1 = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket1.once('connect', resolve);
+      socket1.once('error', reject);
+    });
+
+    // Read greeting
+    await waitForResponse(socket1, '220');
+
+    // Send EHLO
+    socket1.write('EHLO persistence-test\r\n');
+    await waitForResponse(socket1, '250');
+
+    // Start transaction but don't complete it
+    socket1.write('MAIL FROM:<incomplete@example.com>\r\n');
+    const mailResp = await waitForResponse(socket1, '250');
+    expect(mailResp).toInclude('250');
+
+    // Abruptly close connection
+    socket1.destroy();
+    console.log('Abruptly closed connection with incomplete transaction');
+
+    // Wait briefly
+    await new Promise(resolve => setTimeout(resolve, 1000));
+
+    // Create new connection and verify server recovered
+    const socket2 = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket2.once('connect', resolve);
+      socket2.once('error', reject);
+    });
+
+    // Read greeting
+    await waitForResponse(socket2, '220');
+
+    // Send EHLO
+    socket2.write('EHLO recovery-test\r\n');
+    await waitForResponse(socket2, '250');
+
+    // Try new transaction - should work without issues from previous incomplete one
+    socket2.write('MAIL FROM:<recovery@example.com>\r\n');
+    const mailResponse = await waitForResponse(socket2, '250');
+    expect(mailResponse).toInclude('250');
+    console.log('Server recovered successfully - new transaction started without issues');
+
+    socket2.write('QUIT\r\n');
+    await waitForResponse(socket2, '221');
+    socket2.end();
+
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('cleanup server', async () => {
+  await stopTestServer(testServer);
+});
+
+tap.start();

test/suite/smtpserver_reliability/test.rel-03.resource-leak-detection.ts

@@ -0,0 +1,394 @@
+import * as plugins from '@git.zone/tstest/tapbundle';
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as net from 'net';
+import { startTestServer, stopTestServer } from '../../helpers/server.loader.js';
+
+const TEST_PORT = 2525;
+
+let testServer;
+
+interface ResourceMetrics {
+  timestamp: number;
+  memoryUsage: {
+    rss: number;
+    heapTotal: number;
+    heapUsed: number;
+    external: number;
+  };
+  processInfo: {
+    pid: number;
+    uptime: number;
+    cpuUsage: NodeJS.CpuUsage;
+  };
+}
+
+interface LeakAnalysis {
+  memoryGrowthMB: number;
+  memoryTrend: number;
+  stabilityScore: number;
+  memoryLeakDetected: boolean;
+  resourcesStable: boolean;
+  samplesAnalyzed: number;
+  initialMemoryMB: number;
+  finalMemoryMB: number;
+}
+
+const captureResourceMetrics = async (): Promise<ResourceMetrics> => {
+  // Force GC if available before measurement
+  if (global.gc) {
+    global.gc();
+    await new Promise(resolve => setTimeout(resolve, 100));
+  }
+
+  const memUsage = process.memoryUsage();
+  
+  return {
+    timestamp: Date.now(),
+    memoryUsage: {
+      rss: Math.round(memUsage.rss / 1024 / 1024 * 100) / 100,
+      heapTotal: Math.round(memUsage.heapTotal / 1024 / 1024 * 100) / 100,
+      heapUsed: Math.round(memUsage.heapUsed / 1024 / 1024 * 100) / 100,
+      external: Math.round(memUsage.external / 1024 / 1024 * 100) / 100
+    },
+    processInfo: {
+      pid: process.pid,
+      uptime: process.uptime(),
+      cpuUsage: process.cpuUsage()
+    }
+  };
+};
+
+// Helper function to wait for SMTP response
+const waitForResponse = (socket: net.Socket, expectedCode?: string, timeout = 5000): Promise<string> => {
+  return new Promise((resolve, reject) => {
+    let buffer = '';
+    const timer = setTimeout(() => {
+      socket.removeListener('data', handler);
+      reject(new Error(`Timeout waiting for ${expectedCode || 'any'} response`));
+    }, timeout);
+    
+    const handler = (data: Buffer) => {
+      buffer += data.toString();
+      const lines = buffer.split('\r\n');
+      
+      // Check if we have a complete response
+      for (const line of lines) {
+        if (expectedCode) {
+          if (line.startsWith(expectedCode + ' ')) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        } else {
+          // Any complete response line
+          if (line.match(/^\d{3} /)) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        }
+      }
+    };
+    
+    socket.on('data', handler);
+  });
+};
+
+const analyzeResourceLeaks = (initial: ResourceMetrics, samples: Array<{ operation: number; metrics: ResourceMetrics }>, final: ResourceMetrics): LeakAnalysis => {
+  const memoryGrowthMB = final.memoryUsage.heapUsed - initial.memoryUsage.heapUsed;
+  
+  // Analyze memory trend over samples
+  let memoryTrend = 0;
+  if (samples.length > 1) {
+    const firstSample = samples[0].metrics.memoryUsage.heapUsed;
+    const lastSample = samples[samples.length - 1].metrics.memoryUsage.heapUsed;
+    memoryTrend = lastSample - firstSample;
+  }
+  
+  // Calculate stability score based on memory variance
+  let stabilityScore = 1.0;
+  if (samples.length > 2) {
+    const memoryValues = samples.map(s => s.metrics.memoryUsage.heapUsed);
+    const average = memoryValues.reduce((a, b) => a + b, 0) / memoryValues.length;
+    const variance = memoryValues.reduce((acc, val) => acc + Math.pow(val - average, 2), 0) / memoryValues.length;
+    const stdDev = Math.sqrt(variance);
+    stabilityScore = Math.max(0, 1 - (stdDev / average));
+  }
+  
+  return {
+    memoryGrowthMB: Math.round(memoryGrowthMB * 100) / 100,
+    memoryTrend: Math.round(memoryTrend * 100) / 100,
+    stabilityScore: Math.round(stabilityScore * 100) / 100,
+    memoryLeakDetected: memoryGrowthMB > 50,
+    resourcesStable: stabilityScore > 0.8 && memoryGrowthMB < 25,
+    samplesAnalyzed: samples.length,
+    initialMemoryMB: initial.memoryUsage.heapUsed,
+    finalMemoryMB: final.memoryUsage.heapUsed
+  };
+};
+
+tap.test('prepare server', async () => {
+  testServer = await startTestServer({ port: TEST_PORT });
+  await new Promise(resolve => setTimeout(resolve, 100));
+});
+
+tap.test('REL-03: Resource leak detection - Memory leak analysis', async (tools) => {
+  const done = tools.defer();
+  const operationCount = 20;
+  const connections: net.Socket[] = [];
+  const samples: Array<{ operation: number; metrics: ResourceMetrics }> = [];
+
+  try {
+    const initialMetrics = await captureResourceMetrics();
+    console.log(`📊 Initial memory: ${initialMetrics.memoryUsage.heapUsed}MB`);
+
+    for (let i = 0; i < operationCount; i++) {
+      console.log(`🔄 Operation ${i + 1}/${operationCount}...`);
+
+      const socket = net.createConnection({
+        host: 'localhost',
+        port: TEST_PORT,
+        timeout: 30000
+      });
+
+      connections.push(socket);
+
+      await new Promise<void>((resolve, reject) => {
+        socket.once('connect', resolve);
+        socket.once('error', reject);
+      });
+
+      // Read greeting
+      await waitForResponse(socket, '220');
+
+      // Send EHLO
+      socket.write(`EHLO leaktest-${i}\r\n`);
+      await waitForResponse(socket, '250');
+
+      // Complete email transaction
+      socket.write(`MAIL FROM:<sender${i}@example.com>\r\n`);
+      const mailResp = await waitForResponse(socket, '250');
+      expect(mailResp).toInclude('250');
+
+      socket.write(`RCPT TO:<recipient${i}@example.com>\r\n`);
+      const rcptResp = await waitForResponse(socket, '250');
+      expect(rcptResp).toInclude('250');
+
+      socket.write('DATA\r\n');
+      const dataResp = await waitForResponse(socket, '354');
+      expect(dataResp).toInclude('354');
+
+      const emailContent = [
+        `From: sender${i}@example.com`,
+        `To: recipient${i}@example.com`,
+        `Subject: Resource Leak Test ${i + 1}`,
+        `Message-ID: <leak-test-${i}-${Date.now()}@example.com>`,
+        '',
+        `This is resource leak test iteration ${i + 1}.`,
+        '.',
+        ''
+      ].join('\r\n');
+
+      socket.write(emailContent);
+      const sendResp = await waitForResponse(socket, '250');
+      expect(sendResp).toInclude('250');
+
+      socket.write('QUIT\r\n');
+      await waitForResponse(socket, '221');
+      socket.end();
+
+      // Capture metrics every 5 operations
+      if ((i + 1) % 5 === 0) {
+        const metrics = await captureResourceMetrics();
+        samples.push({
+          operation: i + 1,
+          metrics
+        });
+        console.log(`📈 Sample ${samples.length}: Memory ${metrics.memoryUsage.heapUsed}MB`);
+      }
+
+      // Small delay between operations
+      await new Promise(resolve => setTimeout(resolve, 100));
+    }
+
+    // Clean up all connections
+    connections.forEach(conn => {
+      if (!conn.destroyed) {
+        conn.destroy();
+      }
+    });
+
+    // Wait for cleanup
+    await new Promise(resolve => setTimeout(resolve, 2000));
+
+    const finalMetrics = await captureResourceMetrics();
+    const leakAnalysis = analyzeResourceLeaks(initialMetrics, samples, finalMetrics);
+
+    console.log('\n📊 Resource Leak Analysis:');
+    console.log(`Initial memory: ${leakAnalysis.initialMemoryMB}MB`);
+    console.log(`Final memory: ${leakAnalysis.finalMemoryMB}MB`);
+    console.log(`Memory growth: ${leakAnalysis.memoryGrowthMB}MB`);
+    console.log(`Memory trend: ${leakAnalysis.memoryTrend}MB`);
+    console.log(`Stability score: ${leakAnalysis.stabilityScore}`);
+    console.log(`Memory leak detected: ${leakAnalysis.memoryLeakDetected}`);
+    console.log(`Resources stable: ${leakAnalysis.resourcesStable}`);
+
+    expect(leakAnalysis.memoryLeakDetected).toEqual(false);
+    expect(leakAnalysis.resourcesStable).toEqual(true);
+    done.resolve();
+  } catch (error) {
+    connections.forEach(conn => conn.destroy());
+    done.reject(error);
+  }
+});
+
+tap.test('REL-03: Resource leak detection - Connection leak test', async (tools) => {
+  const done = tools.defer();
+  const abandonedConnections: net.Socket[] = [];
+
+  try {
+    console.log('\nTesting for connection resource leaks...');
+
+    // Create connections that are abandoned without proper cleanup
+    for (let i = 0; i < 10; i++) {
+      const socket = net.createConnection({
+        host: 'localhost',
+        port: TEST_PORT,
+        timeout: 30000
+      });
+
+      abandonedConnections.push(socket);
+
+      await new Promise<void>((resolve, reject) => {
+        socket.once('connect', resolve);
+        socket.once('error', reject);
+      });
+
+      // Read greeting but don't complete transaction
+      await new Promise<void>((resolve) => {
+        socket.once('data', () => resolve());
+      });
+
+      // Start but don't complete EHLO
+      socket.write(`EHLO abandoned-${i}\r\n`);
+      
+      // Don't wait for response, just move to next
+      await new Promise(resolve => setTimeout(resolve, 50));
+    }
+
+    console.log('Created 10 abandoned connections');
+
+    // Wait a bit
+    await new Promise(resolve => setTimeout(resolve, 2000));
+
+    // Try to create new connections - should still work
+    let newConnectionsSuccessful = 0;
+    for (let i = 0; i < 5; i++) {
+      try {
+        const socket = net.createConnection({
+          host: 'localhost',
+          port: TEST_PORT,
+          timeout: 5000
+        });
+
+        await new Promise<void>((resolve, reject) => {
+          const timeout = setTimeout(() => {
+            socket.destroy();
+            reject(new Error('Connection timeout'));
+          }, 5000);
+
+          socket.once('connect', () => {
+            clearTimeout(timeout);
+            resolve();
+          });
+          socket.once('error', (err) => {
+            clearTimeout(timeout);
+            reject(err);
+          });
+        });
+
+        // Verify connection works
+        const greeting = await new Promise<string>((resolve) => {
+          socket.once('data', (chunk) => {
+            resolve(chunk.toString());
+          });
+        });
+
+        if (greeting.includes('220')) {
+          newConnectionsSuccessful++;
+          socket.write('QUIT\r\n');
+          socket.end();
+        }
+      } catch (error) {
+        console.log(`New connection ${i + 1} failed:`, error.message);
+      }
+    }
+
+    // Clean up abandoned connections
+    abandonedConnections.forEach(conn => conn.destroy());
+
+    console.log(`New connections successful: ${newConnectionsSuccessful}/5`);
+
+    // Server should still accept new connections despite abandoned ones
+    expect(newConnectionsSuccessful).toBeGreaterThanOrEqual(4);
+    done.resolve();
+  } catch (error) {
+    abandonedConnections.forEach(conn => conn.destroy());
+    done.reject(error);
+  }
+});
+
+tap.test('REL-03: Resource leak detection - Rapid create/destroy cycles', async (tools) => {
+  const done = tools.defer();
+  const cycles = 30;
+  const initialMetrics = await captureResourceMetrics();
+
+  try {
+    console.log('\nTesting rapid connection create/destroy cycles...');
+
+    for (let i = 0; i < cycles; i++) {
+      const socket = net.createConnection({
+        host: 'localhost',
+        port: TEST_PORT,
+        timeout: 5000
+      });
+
+      await new Promise<void>((resolve, reject) => {
+        socket.once('connect', resolve);
+        socket.once('error', reject);
+      });
+
+      // Immediately destroy after connect
+      socket.destroy();
+
+      // Very short delay
+      await new Promise(resolve => setTimeout(resolve, 20));
+
+      if ((i + 1) % 10 === 0) {
+        console.log(`Completed ${i + 1} cycles`);
+      }
+    }
+
+    // Wait for resources to be released
+    await new Promise(resolve => setTimeout(resolve, 3000));
+
+    const finalMetrics = await captureResourceMetrics();
+    const memoryGrowth = finalMetrics.memoryUsage.heapUsed - initialMetrics.memoryUsage.heapUsed;
+
+    console.log(`Memory growth after ${cycles} cycles: ${memoryGrowth.toFixed(2)}MB`);
+
+    // Memory growth should be minimal
+    expect(memoryGrowth).toBeLessThan(10);
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('cleanup server', async () => {
+  await stopTestServer(testServer);
+});
+
+tap.start();

test/suite/smtpserver_reliability/test.rel-04.error-recovery.ts

@@ -0,0 +1,401 @@
+import * as plugins from '@git.zone/tstest/tapbundle';
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as net from 'net';
+import { startTestServer, stopTestServer } from '../../helpers/server.loader.js';
+
+const TEST_PORT = 2525;
+
+let testServer;
+
+const createConnection = async (): Promise<net.Socket> => {
+  const socket = net.createConnection({
+    host: 'localhost',
+    port: TEST_PORT,
+    timeout: 5000
+  });
+
+  await new Promise<void>((resolve, reject) => {
+    socket.once('connect', resolve);
+    socket.once('error', reject);
+  });
+
+  return socket;
+};
+
+// Helper function to wait for SMTP response
+const waitForResponse = (socket: net.Socket, expectedCode?: string, timeout = 5000): Promise<string> => {
+  return new Promise((resolve, reject) => {
+    let buffer = '';
+    const timer = setTimeout(() => {
+      socket.removeListener('data', handler);
+      reject(new Error(`Timeout waiting for ${expectedCode || 'any'} response`));
+    }, timeout);
+    
+    const handler = (data: Buffer) => {
+      buffer += data.toString();
+      const lines = buffer.split('\r\n');
+      
+      // Check if we have a complete response
+      for (const line of lines) {
+        if (expectedCode) {
+          if (line.startsWith(expectedCode + ' ')) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        } else {
+          // Any complete response line
+          if (line.match(/^\d{3} /)) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        }
+      }
+    };
+    
+    socket.on('data', handler);
+  });
+};
+
+const getResponse = waitForResponse;
+
+const testBasicSmtpFlow = async (socket: net.Socket): Promise<boolean> => {
+  try {
+    // Read greeting
+    await waitForResponse(socket, '220');
+
+    // Send EHLO
+    socket.write('EHLO recovery-test\r\n');
+    const ehloResp = await waitForResponse(socket, '250');
+    if (!ehloResp.includes('250')) return false;
+
+    socket.write('MAIL FROM:<sender@example.com>\r\n');
+    const mailResp = await waitForResponse(socket, '250');
+    if (!mailResp.includes('250')) return false;
+
+    socket.write('RCPT TO:<recipient@example.com>\r\n');
+    const rcptResp = await waitForResponse(socket, '250');
+    if (!rcptResp.includes('250')) return false;
+
+    socket.write('DATA\r\n');
+    const dataResp = await waitForResponse(socket, '354');
+    if (!dataResp.includes('354')) return false;
+
+    const testEmail = [
+      'From: sender@example.com',
+      'To: recipient@example.com',
+      'Subject: Recovery Test Email',
+      '',
+      'This email tests server recovery.',
+      '.',
+      ''
+    ].join('\r\n');
+
+    socket.write(testEmail);
+    const finalResp = await waitForResponse(socket, '250');
+
+    socket.write('QUIT\r\n');
+    socket.end();
+
+    return finalResp.includes('250');
+  } catch (error) {
+    console.log('Basic SMTP flow error:', error);
+    return false;
+  }
+};
+
+tap.test('prepare server', async () => {
+  testServer = await startTestServer({ port: TEST_PORT });
+  await new Promise(resolve => setTimeout(resolve, 100));
+});
+
+tap.test('REL-04: Error recovery - Invalid command recovery', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('Testing recovery from invalid commands...');
+
+    // Phase 1: Send invalid commands
+    const socket1 = await createConnection();
+    await waitForResponse(socket1, '220');
+
+    // Send multiple invalid commands
+    socket1.write('INVALID_COMMAND\r\n');
+    const response1 = await waitForResponse(socket1);
+    expect(response1).toMatch(/50[0-3]/); // Should get error response
+
+    socket1.write('ANOTHER_INVALID\r\n');
+    const response2 = await waitForResponse(socket1);
+    expect(response2).toMatch(/50[0-3]/);
+
+    socket1.write('YET_ANOTHER_BAD_CMD\r\n');
+    const response3 = await waitForResponse(socket1);
+    expect(response3).toMatch(/50[0-3]/);
+
+    socket1.end();
+
+    // Phase 2: Test recovery - server should still work normally
+    await new Promise(resolve => setTimeout(resolve, 500));
+    
+    const socket2 = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(socket2);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from invalid commands');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-04: Error recovery - Malformed data recovery', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting recovery from malformed data...');
+
+    // Phase 1: Send malformed data
+    const socket1 = await createConnection();
+    await waitForResponse(socket1, '220');
+
+    socket1.write('EHLO testhost\r\n');
+    await waitForResponse(socket1, '250');
+
+    // Send malformed MAIL FROM
+    socket1.write('MAIL FROM: invalid-format\r\n');
+    const response1 = await waitForResponse(socket1);
+    expect(response1).toMatch(/50[0-3]/);
+
+    // Send malformed RCPT TO
+    socket1.write('RCPT TO: also-invalid\r\n');
+    const response2 = await waitForResponse(socket1);
+    expect(response2).toMatch(/50[0-3]/);
+
+    // Send malformed DATA with binary
+    socket1.write('DATA\x00\x01\x02CORRUPTED\r\n');
+    const response3 = await waitForResponse(socket1);
+    expect(response3).toMatch(/50[0-3]/);
+
+    socket1.end();
+
+    // Phase 2: Test recovery
+    await new Promise(resolve => setTimeout(resolve, 500));
+    
+    const socket2 = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(socket2);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from malformed data');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-04: Error recovery - Premature disconnection recovery', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting recovery from premature disconnection...');
+
+    // Phase 1: Create incomplete transactions
+    for (let i = 0; i < 3; i++) {
+      const socket = await createConnection();
+      await waitForResponse(socket, '220');
+
+      socket.write('EHLO abrupt-test\r\n');
+      await waitForResponse(socket, '250');
+
+      socket.write('MAIL FROM:<test@example.com>\r\n');
+      await waitForResponse(socket, '250');
+
+      // Abruptly close connection during transaction
+      socket.destroy();
+      console.log(`  Abruptly closed connection ${i + 1}`);
+
+      await new Promise(resolve => setTimeout(resolve, 200));
+    }
+
+    // Phase 2: Test recovery
+    await new Promise(resolve => setTimeout(resolve, 1000));
+    
+    const socket2 = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(socket2);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from premature disconnections');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-04: Error recovery - Data corruption recovery', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting recovery from data corruption...');
+
+    const socket1 = await createConnection();
+    await waitForResponse(socket1, '220');
+
+    socket1.write('EHLO corruption-test\r\n');
+    await waitForResponse(socket1, '250');
+
+    socket1.write('MAIL FROM:<sender@example.com>\r\n');
+    await waitForResponse(socket1, '250');
+
+    socket1.write('RCPT TO:<recipient@example.com>\r\n');
+    await waitForResponse(socket1, '250');
+
+    socket1.write('DATA\r\n');
+    const dataResp = await waitForResponse(socket1, '354');
+    expect(dataResp).toInclude('354');
+
+    // Send corrupted email data with null bytes and invalid characters
+    socket1.write('From: test\r\n\0\0\0CORRUPTED DATA\xff\xfe\r\n');
+    socket1.write('Subject: \x01\x02\x03Invalid\r\n');
+    socket1.write('\r\n');
+    socket1.write('Body with \0null bytes\r\n');
+    socket1.write('.\r\n');
+
+    try {
+      const response = await waitForResponse(socket1);
+      console.log('  Server response to corrupted data:', response.substring(0, 50));
+    } catch (error) {
+      console.log('  Server rejected corrupted data (expected)');
+    }
+
+    socket1.end();
+
+    // Phase 2: Test recovery
+    await new Promise(resolve => setTimeout(resolve, 1000));
+    
+    const socket2 = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(socket2);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from data corruption');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-04: Error recovery - Connection flooding recovery', async (tools) => {
+  const done = tools.defer();
+  const connections: net.Socket[] = [];
+
+  try {
+    console.log('\nTesting recovery from connection flooding...');
+
+    // Phase 1: Create multiple rapid connections
+    console.log('  Creating 15 rapid connections...');
+    for (let i = 0; i < 15; i++) {
+      try {
+        const socket = net.createConnection({
+          host: 'localhost',
+          port: TEST_PORT,
+          timeout: 2000
+        });
+        connections.push(socket);
+        
+        // Don't wait for connection to complete
+        await new Promise(resolve => setTimeout(resolve, 50));
+      } catch (error) {
+        // Some connections might fail - that's expected
+        console.log(`  Connection ${i + 1} failed (expected during flooding)`);
+      }
+    }
+
+    console.log(`  Created ${connections.length} connections`);
+
+    // Close all connections
+    connections.forEach(conn => {
+      try {
+        conn.destroy();
+      } catch (e) {
+        // Ignore errors
+      }
+    });
+
+    // Phase 2: Test recovery
+    console.log('  Waiting for server to recover...');
+    await new Promise(resolve => setTimeout(resolve, 3000));
+    
+    const socket2 = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(socket2);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from connection flooding');
+    done.resolve();
+  } catch (error) {
+    connections.forEach(conn => conn.destroy());
+    done.reject(error);
+  }
+});
+
+tap.test('REL-04: Error recovery - Mixed error scenario', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting recovery from mixed error scenarios...');
+
+    // Create multiple error conditions simultaneously
+    const errorPromises = [];
+
+    // Invalid command connection
+    errorPromises.push((async () => {
+      const socket = await createConnection();
+      await waitForResponse(socket, '220');
+      socket.write('TOTALLY_WRONG\r\n');
+      await waitForResponse(socket);
+      socket.destroy();
+    })());
+
+    // Malformed data connection
+    errorPromises.push((async () => {
+      const socket = await createConnection();
+      await waitForResponse(socket, '220');
+      socket.write('MAIL FROM:<<<invalid>>>\r\n');
+      try {
+        await waitForResponse(socket);
+      } catch (e) {
+        // Expected
+      }
+      socket.destroy();
+    })());
+
+    // Abrupt disconnection
+    errorPromises.push((async () => {
+      const socket = await createConnection();
+      socket.destroy();
+    })());
+
+    // Wait for all errors to execute
+    await Promise.allSettled(errorPromises);
+
+    console.log('  All error scenarios executed');
+
+    // Test recovery
+    await new Promise(resolve => setTimeout(resolve, 2000));
+    
+    const socket = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(socket);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from mixed error scenarios');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('cleanup server', async () => {
+  await stopTestServer(testServer);
+});
+
+tap.start();

test/suite/smtpserver_reliability/test.rel-05.dns-resolution-failure.ts

@@ -0,0 +1,335 @@
+import * as plugins from '@git.zone/tstest/tapbundle';
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as net from 'net';
+import { startTestServer, stopTestServer } from '../../helpers/server.loader.js';
+
+const TEST_PORT = 2525;
+
+let testServer;
+
+interface DnsTestResult {
+  scenario: string;
+  domain: string;
+  expectedBehavior: string;
+  mailFromSuccess: boolean;
+  rcptToSuccess: boolean;
+  mailFromResponse: string;
+  rcptToResponse: string;
+  handledGracefully: boolean;
+}
+
+// Helper function to wait for SMTP response
+const waitForResponse = (socket: net.Socket, expectedCode?: string, timeout = 5000): Promise<string> => {
+  return new Promise((resolve, reject) => {
+    let buffer = '';
+    const timer = setTimeout(() => {
+      socket.removeListener('data', handler);
+      reject(new Error(`Timeout waiting for ${expectedCode || 'any'} response`));
+    }, timeout);
+    
+    const handler = (data: Buffer) => {
+      buffer += data.toString();
+      const lines = buffer.split('\r\n');
+      
+      // Check if we have a complete response
+      for (const line of lines) {
+        if (expectedCode) {
+          if (line.startsWith(expectedCode + ' ')) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        } else {
+          // Any complete response line
+          if (line.match(/^\d{3} /)) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        }
+      }
+    };
+    
+    socket.on('data', handler);
+  });
+};
+
+tap.test('prepare server', async () => {
+  testServer = await startTestServer({ port: TEST_PORT });
+  await new Promise(resolve => setTimeout(resolve, 100));
+});
+
+tap.test('REL-05: DNS resolution failure handling - Non-existent domains', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    const socket = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket.once('connect', resolve);
+      socket.once('error', reject);
+    });
+
+    // Read greeting
+    await waitForResponse(socket, '220');
+
+    // Send EHLO
+    socket.write('EHLO dns-test\r\n');
+    await waitForResponse(socket, '250');
+
+    console.log('Testing DNS resolution for non-existent domains...');
+
+    // Test 1: Non-existent domain in MAIL FROM
+    socket.write('MAIL FROM:<sender@non-existent-domain-12345.invalid>\r\n');
+    const mailResponse = await waitForResponse(socket);
+
+    console.log('  MAIL FROM response:', mailResponse.trim());
+    
+    // Server should either accept (and defer later) or reject immediately
+    const mailFromHandled = mailResponse.includes('250') || 
+                           mailResponse.includes('450') || 
+                           mailResponse.includes('550');
+    expect(mailFromHandled).toEqual(true);
+
+    // Reset if needed
+    if (mailResponse.includes('250')) {
+      socket.write('RSET\r\n');
+      await waitForResponse(socket, '250');
+    }
+
+    // Test 2: Non-existent domain in RCPT TO
+    socket.write('MAIL FROM:<sender@example.com>\r\n');
+    const mailFromResp = await waitForResponse(socket, '250');
+    expect(mailFromResp).toInclude('250');
+
+    socket.write('RCPT TO:<recipient@non-existent-domain-xyz.invalid>\r\n');
+    const rcptResponse = await waitForResponse(socket);
+
+    console.log('  RCPT TO response:', rcptResponse.trim());
+    
+    // Server may accept (and defer validation) or reject immediately
+    const rcptToHandled = rcptResponse.includes('250') || // Accepted (for later validation)
+                         rcptResponse.includes('450') || // Temporary failure
+                         rcptResponse.includes('550') || // Permanent failure
+                         rcptResponse.includes('553');   // Address error
+    expect(rcptToHandled).toEqual(true);
+
+    socket.write('QUIT\r\n');
+    socket.end();
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-05: DNS resolution failure handling - Malformed domains', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    const socket = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket.once('connect', resolve);
+      socket.once('error', reject);
+    });
+
+    // Read greeting
+    await waitForResponse(socket, '220');
+
+    // Send EHLO
+    socket.write('EHLO malformed-test\r\n');
+    await waitForResponse(socket, '250');
+
+    console.log('\nTesting malformed domain handling...');
+
+    const malformedDomains = [
+      'malformed..domain..test',
+      'invalid-.domain.com',
+      'domain.with.spaces .com',
+      '.leading-dot.com',
+      'trailing-dot.com.',
+      'domain@with@at.com',
+      'a'.repeat(255) + '.toolong.com' // Domain too long
+    ];
+
+    for (const domain of malformedDomains) {
+      console.log(`  Testing: ${domain.substring(0, 50)}${domain.length > 50 ? '...' : ''}`);
+
+      socket.write(`MAIL FROM:<test@${domain}>\r\n`);
+      const response = await waitForResponse(socket);
+
+      // Server should reject malformed domains or accept for later validation
+      const properlyHandled = response.includes('250') || // Accepted (may validate later)
+                             response.includes('501') || // Syntax error
+                             response.includes('550') || // Rejected
+                             response.includes('553');   // Address error
+      
+      console.log(`    Response: ${response.trim().substring(0, 50)}`);
+      expect(properlyHandled).toEqual(true);
+
+      // Reset if needed
+      if (!response.includes('5')) {
+        socket.write('RSET\r\n');
+        await waitForResponse(socket, '250');
+      }
+    }
+
+    socket.write('QUIT\r\n');
+    socket.end();
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-05: DNS resolution failure handling - Special cases', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    const socket = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket.once('connect', resolve);
+      socket.once('error', reject);
+    });
+
+    // Read greeting
+    await waitForResponse(socket, '220');
+
+    // Send EHLO
+    socket.write('EHLO special-test\r\n');
+    await waitForResponse(socket, '250');
+
+    console.log('\nTesting special DNS cases...');
+
+    // Test 1: Localhost (may be accepted or rejected)
+    socket.write('MAIL FROM:<sender@localhost>\r\n');
+    const localhostResponse = await waitForResponse(socket);
+
+    console.log('  Localhost response:', localhostResponse.trim());
+    const localhostHandled = localhostResponse.includes('250') || localhostResponse.includes('501');
+    expect(localhostHandled).toEqual(true);
+
+    // Only reset if transaction was started
+    if (localhostResponse.includes('250')) {
+      socket.write('RSET\r\n');
+      await waitForResponse(socket, '250');
+    }
+
+    // Test 2: IP address (should work)
+    socket.write('MAIL FROM:<sender@[127.0.0.1]>\r\n');
+    const ipResponse = await waitForResponse(socket);
+
+    console.log('  IP address response:', ipResponse.trim());
+    const ipHandled = ipResponse.includes('250') || ipResponse.includes('501');
+    expect(ipHandled).toEqual(true);
+
+    // Only reset if transaction was started
+    if (ipResponse.includes('250')) {
+      socket.write('RSET\r\n');
+      await waitForResponse(socket, '250');
+    }
+
+    // Test 3: Empty domain
+    socket.write('MAIL FROM:<sender@>\r\n');
+    const emptyResponse = await waitForResponse(socket);
+
+    console.log('  Empty domain response:', emptyResponse.trim());
+    expect(emptyResponse).toMatch(/50[1-3]/); // Should reject
+
+    socket.write('QUIT\r\n');
+    socket.end();
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-05: DNS resolution failure handling - Mixed valid/invalid recipients', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    const socket = net.createConnection({
+      host: 'localhost',
+      port: TEST_PORT,
+      timeout: 30000
+    });
+
+    await new Promise<void>((resolve, reject) => {
+      socket.once('connect', resolve);
+      socket.once('error', reject);
+    });
+
+    // Read greeting
+    await waitForResponse(socket, '220');
+
+    // Send EHLO
+    socket.write('EHLO mixed-test\r\n');
+    await waitForResponse(socket, '250');
+
+    console.log('\nTesting mixed valid/invalid recipients...');
+
+    // Start transaction
+    socket.write('MAIL FROM:<sender@example.com>\r\n');
+    const mailFromResp = await waitForResponse(socket, '250');
+    expect(mailFromResp).toInclude('250');
+
+    // Add valid recipient
+    socket.write('RCPT TO:<valid@example.com>\r\n');
+    const validRcptResponse = await waitForResponse(socket, '250');
+
+    console.log('  Valid recipient:', validRcptResponse.trim());
+    expect(validRcptResponse).toInclude('250');
+
+    // Add invalid recipient
+    socket.write('RCPT TO:<invalid@non-existent-domain-abc.invalid>\r\n');
+    const invalidRcptResponse = await waitForResponse(socket);
+
+    console.log('  Invalid recipient:', invalidRcptResponse.trim());
+    
+    // Server may accept (for later validation) or reject invalid domain
+    const invalidHandled = invalidRcptResponse.includes('250') || // Accepted (for later validation)
+                          invalidRcptResponse.includes('450') || 
+                          invalidRcptResponse.includes('550') ||
+                          invalidRcptResponse.includes('553');
+    expect(invalidHandled).toEqual(true);
+
+    // Try to send data (should work if at least one valid recipient)
+    socket.write('DATA\r\n');
+    const dataResponse = await waitForResponse(socket);
+
+    if (dataResponse.includes('354')) {
+      socket.write('Subject: Mixed recipient test\r\n\r\nTest\r\n.\r\n');
+      await waitForResponse(socket, '250');
+      console.log('  Message accepted with valid recipient');
+    } else {
+      console.log('  Server rejected DATA (acceptable behavior)');
+    }
+
+    socket.write('QUIT\r\n');
+    socket.end();
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('cleanup server', async () => {
+  await stopTestServer(testServer);
+});
+
+tap.start();

test/suite/smtpserver_reliability/test.rel-06.network-interruption.ts

@@ -0,0 +1,410 @@
+import * as plugins from '@git.zone/tstest/tapbundle';
+import { expect, tap } from '@git.zone/tstest/tapbundle';
+import * as net from 'net';
+import { startTestServer, stopTestServer } from '../../helpers/server.loader.js';
+
+const TEST_PORT = 2525;
+
+let testServer;
+
+const createConnection = async (): Promise<net.Socket> => {
+  const socket = net.createConnection({
+    host: 'localhost',
+    port: TEST_PORT,
+    timeout: 5000
+  });
+
+  await new Promise<void>((resolve, reject) => {
+    socket.once('connect', resolve);
+    socket.once('error', reject);
+  });
+
+  return socket;
+};
+
+// Helper function to wait for SMTP response
+const waitForResponse = (socket: net.Socket, expectedCode?: string, timeout = 5000): Promise<string> => {
+  return new Promise((resolve, reject) => {
+    let buffer = '';
+    const timer = setTimeout(() => {
+      socket.removeListener('data', handler);
+      reject(new Error(`Timeout waiting for ${expectedCode || 'any'} response`));
+    }, timeout);
+    
+    const handler = (data: Buffer) => {
+      buffer += data.toString();
+      const lines = buffer.split('\r\n');
+      
+      // Check if we have a complete response
+      for (const line of lines) {
+        if (expectedCode) {
+          if (line.startsWith(expectedCode + ' ')) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        } else {
+          // Any complete response line
+          if (line.match(/^\d{3} /)) {
+            clearTimeout(timer);
+            socket.removeListener('data', handler);
+            resolve(buffer);
+            return;
+          }
+        }
+      }
+    };
+    
+    socket.on('data', handler);
+  });
+};
+
+const getResponse = waitForResponse;
+
+const testBasicSmtpFlow = async (socket: net.Socket): Promise<boolean> => {
+  try {
+    await waitForResponse(socket, '220');
+
+    socket.write('EHLO test.example.com\r\n');
+    const ehloResp = await waitForResponse(socket, '250');
+    if (!ehloResp.includes('250')) return false;
+
+    socket.write('MAIL FROM:<test@example.com>\r\n');
+    const mailResp = await waitForResponse(socket, '250');
+    if (!mailResp.includes('250')) return false;
+
+    socket.write('RCPT TO:<recipient@example.com>\r\n');
+    const rcptResp = await waitForResponse(socket, '250');
+    if (!rcptResp.includes('250')) return false;
+
+    socket.write('DATA\r\n');
+    const dataResp = await waitForResponse(socket, '354');
+    if (!dataResp.includes('354')) return false;
+
+    const testEmail = [
+      'From: test@example.com',
+      'To: recipient@example.com',
+      'Subject: Interruption Recovery Test',
+      '',
+      'This email tests server recovery after network interruption.',
+      '.',
+      ''
+    ].join('\r\n');
+
+    socket.write(testEmail);
+    const finalResp = await waitForResponse(socket, '250');
+
+    socket.write('QUIT\r\n');
+    socket.end();
+
+    return finalResp.includes('250');
+  } catch (error) {
+    return false;
+  }
+};
+
+tap.test('prepare server', async () => {
+  testServer = await startTestServer({ port: TEST_PORT });
+  await new Promise(resolve => setTimeout(resolve, 100));
+});
+
+tap.test('REL-06: Network interruption - Sudden connection drop', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('Testing sudden connection drop during session...');
+
+    // Phase 1: Create connection and drop it mid-session
+    const socket1 = await createConnection();
+    await waitForResponse(socket1, '220');
+
+    socket1.write('EHLO testhost\r\n');
+    await waitForResponse(socket1, '250');
+
+    socket1.write('MAIL FROM:<sender@example.com>\r\n');
+    await waitForResponse(socket1, '250');
+
+    // Abruptly close connection during active session
+    socket1.destroy();
+    console.log('  Connection abruptly closed');
+
+    // Phase 2: Test recovery
+    await new Promise(resolve => setTimeout(resolve, 1000));
+
+    const socket2 = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(socket2);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from sudden connection drop');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-06: Network interruption - Data transfer interruption', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting connection interruption during data transfer...');
+
+    const socket = await createConnection();
+    await waitForResponse(socket, '220');
+
+    socket.write('EHLO datatest\r\n');
+    await waitForResponse(socket, '250');
+
+    socket.write('MAIL FROM:<sender@example.com>\r\n');
+    await waitForResponse(socket, '250');
+
+    socket.write('RCPT TO:<recipient@example.com>\r\n');
+    await waitForResponse(socket, '250');
+
+    socket.write('DATA\r\n');
+    const dataResp = await waitForResponse(socket, '354');
+    expect(dataResp).toInclude('354');
+
+    // Start sending data but interrupt midway
+    socket.write('From: sender@example.com\r\n');
+    socket.write('To: recipient@example.com\r\n');
+    socket.write('Subject: Interruption Test\r\n\r\n');
+    socket.write('This email will be interrupted...\r\n');
+
+    // Wait briefly then destroy connection (simulating network loss)
+    await new Promise(resolve => setTimeout(resolve, 500));
+    socket.destroy();
+    console.log('  Connection interrupted during data transfer');
+
+    // Test recovery
+    await new Promise(resolve => setTimeout(resolve, 1500));
+
+    const newSocket = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(newSocket);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from data transfer interruption');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-06: Network interruption - Rapid reconnection attempts', async (tools) => {
+  const done = tools.defer();
+  const connections: net.Socket[] = [];
+
+  try {
+    console.log('\nTesting rapid reconnection after interruptions...');
+
+    // Create and immediately destroy multiple connections
+    console.log('  Creating 5 unstable connections...');
+    for (let i = 0; i < 5; i++) {
+      try {
+        const socket = net.createConnection({
+          host: 'localhost',
+          port: TEST_PORT,
+          timeout: 2000
+        });
+        
+        connections.push(socket);
+        
+        // Destroy after short random delay to simulate instability
+        setTimeout(() => socket.destroy(), 50 + Math.random() * 150);
+        
+        await new Promise(resolve => setTimeout(resolve, 50));
+      } catch (error) {
+        // Expected - some connections might fail
+      }
+    }
+
+    // Wait for cleanup
+    await new Promise(resolve => setTimeout(resolve, 2000));
+
+    // Now test if server can handle normal connections
+    let successfulConnections = 0;
+    console.log('  Testing recovery with stable connections...');
+    
+    for (let i = 0; i < 3; i++) {
+      try {
+        const socket = await createConnection();
+        const success = await testBasicSmtpFlow(socket);
+        
+        if (success) {
+          successfulConnections++;
+        }
+      } catch (error) {
+        console.log(`  Connection ${i + 1} failed:`, error.message);
+      }
+      
+      await new Promise(resolve => setTimeout(resolve, 500));
+    }
+
+    const recoveryRate = successfulConnections / 3;
+    console.log(`  Recovery rate: ${successfulConnections}/3 (${(recoveryRate * 100).toFixed(0)}%)`);
+
+    expect(recoveryRate).toBeGreaterThanOrEqual(0.66); // At least 2/3 should succeed
+    console.log('✓ Server recovered from rapid reconnection attempts');
+    done.resolve();
+  } catch (error) {
+    connections.forEach(conn => conn.destroy());
+    done.reject(error);
+  }
+});
+
+tap.test('REL-06: Network interruption - Partial command interruption', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting partial command transmission interruption...');
+
+    const socket = await createConnection();
+    await waitForResponse(socket, '220');
+
+    // Send partial EHLO command and interrupt
+    socket.write('EH');
+    console.log('  Sent partial command "EH"');
+    
+    await new Promise(resolve => setTimeout(resolve, 100));
+    socket.destroy();
+    console.log('  Connection destroyed with incomplete command');
+
+    // Test recovery
+    await new Promise(resolve => setTimeout(resolve, 1000));
+
+    const newSocket = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(newSocket);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered from partial command interruption');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-06: Network interruption - Multiple interruption types', async (tools) => {
+  const done = tools.defer();
+  const results: Array<{ type: string; recovered: boolean }> = [];
+
+  try {
+    console.log('\nTesting recovery from multiple interruption types...');
+
+    // Test 1: Interrupt after greeting
+    try {
+      const socket = await createConnection();
+      await waitForResponse(socket, '220');
+      socket.destroy();
+      results.push({ type: 'after-greeting', recovered: false });
+    } catch (e) {
+      results.push({ type: 'after-greeting', recovered: false });
+    }
+
+    await new Promise(resolve => setTimeout(resolve, 500));
+
+    // Test 2: Interrupt during EHLO
+    try {
+      const socket = await createConnection();
+      await waitForResponse(socket, '220');
+      socket.write('EHLO te');
+      socket.destroy();
+      results.push({ type: 'during-ehlo', recovered: false });
+    } catch (e) {
+      results.push({ type: 'during-ehlo', recovered: false });
+    }
+
+    await new Promise(resolve => setTimeout(resolve, 500));
+
+    // Test 3: Interrupt with invalid data
+    try {
+      const socket = await createConnection();
+      await waitForResponse(socket, '220');
+      socket.write('\x00\x01\x02\x03');
+      socket.destroy();
+      results.push({ type: 'invalid-data', recovered: false });
+    } catch (e) {
+      results.push({ type: 'invalid-data', recovered: false });
+    }
+
+    await new Promise(resolve => setTimeout(resolve, 1000));
+
+    // Test final recovery
+    try {
+      const socket = await createConnection();
+      const success = await testBasicSmtpFlow(socket);
+      
+      if (success) {
+        // Mark all previous tests as recovered
+        results.forEach(r => r.recovered = true);
+      }
+    } catch (error) {
+      console.log('Final recovery failed:', error.message);
+    }
+
+    const recoveredCount = results.filter(r => r.recovered).length;
+    console.log(`\nInterruption recovery summary:`);
+    results.forEach(r => {
+      console.log(`  ${r.type}: ${r.recovered ? 'recovered' : 'failed'}`);
+    });
+
+    expect(recoveredCount).toBeGreaterThan(0);
+    console.log(`✓ Server recovered from ${recoveredCount}/${results.length} interruption scenarios`);
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('REL-06: Network interruption - Long delay recovery', async (tools) => {
+  const done = tools.defer();
+
+  try {
+    console.log('\nTesting recovery after long network interruption...');
+
+    // Create connection and start transaction
+    const socket = await createConnection();
+    await waitForResponse(socket, '220');
+
+    socket.write('EHLO longdelay\r\n');
+    await waitForResponse(socket, '250');
+
+    socket.write('MAIL FROM:<sender@example.com>\r\n');
+    await waitForResponse(socket, '250');
+
+    // Simulate long network interruption
+    socket.pause();
+    console.log('  Connection paused (simulating network freeze)');
+    
+    await new Promise(resolve => setTimeout(resolve, 5000)); // 5 second "freeze"
+    
+    // Try to continue - should fail
+    socket.resume();
+    socket.write('RCPT TO:<recipient@example.com>\r\n');
+    
+    let continuationFailed = false;
+    try {
+      await waitForResponse(socket, '250', 3000);
+    } catch (error) {
+      continuationFailed = true;
+      console.log('  Continuation failed as expected');
+    }
+
+    socket.destroy();
+
+    // Test recovery with new connection
+    const newSocket = await createConnection();
+    const recoverySuccess = await testBasicSmtpFlow(newSocket);
+
+    expect(recoverySuccess).toEqual(true);
+    console.log('✓ Server recovered after long network interruption');
+    done.resolve();
+  } catch (error) {
+    done.reject(error);
+  }
+});
+
+tap.test('cleanup server', async () => {
+  await stopTestServer(testServer);
+});
+
+tap.start();