Postmark Webhooks

When to Use This Skill

• Setting up Postmark webhook handlers for email event tracking
• Processing email delivery events (bounce, delivered, open, click)
• Handling spam complaints and subscription changes
• Implementing email engagement analytics
• Troubleshooting webhook authentication issues

Essential Code

Authentication

Postmark does NOT use signature verification. Instead, webhooks are authenticated by including credentials in the webhook URL itself.

// Express - Basic Auth in URL
// Configure webhook URL in Postmark as:
// https://username:[email protected]/webhooks/postmark

app.post('/webhooks/postmark', express.json(), (req, res) => {
  // Basic auth is handled by your web server or proxy
  // Additional validation can check expected payload structure

  const event = req.body;

  // Validate expected fields exist
  if (!event.RecordType || !event.MessageID) {
    return res.status(400).send('Invalid payload structure');
  }

  // Process event
  console.log(`Received ${event.RecordType} event for ${event.Email}`);

  res.sendStatus(200);
});

// Alternative: Token in URL
// Configure webhook URL as:
// https://yourdomain.com/webhooks/postmark?token=your-secret-token

app.post('/webhooks/postmark', express.json(), (req, res) => {
  const token = req.query.token;

  if (token !== process.env.POSTMARK_WEBHOOK_TOKEN) {
    return res.status(401).send('Unauthorized');
  }

  const event = req.body;
  console.log(`Received ${event.RecordType} event`);

  res.sendStatus(200);
});

Handling Multiple Events

// Postmark sends one event per request (not batched)
app.post('/webhooks/postmark', express.json(), (req, res) => {
  const event = req.body;

  switch (event.RecordType) {
    case 'Bounce':
      console.log(`Bounce: ${event.Email} - ${event.Type} - ${event.Description}`);
      // Update contact as undeliverable
      break;

    case 'SpamComplaint':
      console.log(`Spam complaint: ${event.Email}`);
      // Remove from mailing list
      break;

    case 'Open':
      console.log(`Email opened: ${event.Email} at ${event.ReceivedAt}`);
      // Track engagement
      break;

    case 'Click':
      console.log(`Link clicked: ${event.Email} - ${event.OriginalLink}`);
      // Track click-through rate
      break;

    case 'Delivery':
      console.log(`Delivered: ${event.Email} at ${event.DeliveredAt}`);
      // Confirm delivery
      break;

    case 'SubscriptionChange':
      console.log(`Subscription change: ${event.Email} - ${event.ChangedAt}`);
      // Update subscription preferences
      break;

    case 'Inbound':
      console.log(`Inbound email from: ${event.Email} - Subject: ${event.Subject}`);
      // Process incoming email
      break;

    case 'SMTP API Error':
      console.log(`SMTP API error: ${event.Email} - ${event.Error}`);
      // Handle API error, maybe retry
      break;

    default:
      console.log(`Unknown event type: ${event.RecordType}`);
  }

  res.sendStatus(200);
});

Common Event Types

Environment Variables

# For token-based authentication
POSTMARK_WEBHOOK_TOKEN="your-secret-token-here"

# For basic auth (if not using URL-embedded credentials)
WEBHOOK_USERNAME="your-username"
WEBHOOK_PASSWORD="your-password"

Security Best Practices

1. Always use HTTPS - Never configure webhooks with HTTP URLs
2. Use strong credentials - Generate long, random tokens or passwords
3. Validate payload structure - Check for expected fields before processing
4. Implement IP allowlisting - Postmark publishes their IP ranges
5. Consider using a webhook gateway - Like Hookdeck for additional security layers

Local Development

For local webhook testing, use Hookdeck CLI:

npx hookdeck-cli listen 3000 postmark --path /webhooks/postmark

No account required. Provides local tunnel + web UI for inspecting requests.

Resources

• overview.md - What Postmark webhooks are, common event types
• setup.md - Configure webhooks in Postmark dashboard
• verification.md - Authentication methods and security best practices
• examples/ - Complete implementations for Express, Next.js, and FastAPI

Recommended: webhook-handler-patterns

For production-ready webhook handling, also install the webhook-handler-patterns skill:

• Handler sequence - Webhook processing flow
• Idempotency - Prevent duplicate processing
• Error handling - Graceful error recovery
• Retry logic - Handle transient failures

Related Skills

• sendgrid-webhooks - SendGrid webhook handling with ECDSA verification
• resend-webhooks - Resend webhook handling with Svix signatures
• stripe-webhooks - Stripe webhook handling with HMAC-SHA256
• webhook-handler-patterns - Idempotency, error handling, retry logic
• hookdeck-event-gateway - Production webhook infrastructure