SendGrid Webhooks

When to Use This Skill

• Setting up SendGrid webhook handlers for email delivery tracking
• Debugging ECDSA signature verification failures
• Processing email events (bounce, delivered, open, click, spam report)
• Implementing email engagement analytics

Essential Code

Signature Verification (Manual)

SendGrid uses ECDSA (Elliptic Curve Digital Signature Algorithm) with public key verification.

// Node.js manual verification
const crypto = require('crypto');

function verifySignature(publicKey, payload, signature, timestamp) {
  // Decode the base64 signature
  const decodedSignature = Buffer.from(signature, 'base64');

  // Create the signed content
  const signedContent = timestamp + payload;

  // Create verifier
  const verifier = crypto.createVerify('sha256');
  verifier.update(signedContent);

  // Add PEM headers if not present
  let pemKey = publicKey;
  if (!pemKey.includes('BEGIN PUBLIC KEY')) {
    pemKey = `-----BEGIN PUBLIC KEY-----\n${publicKey}\n-----END PUBLIC KEY-----`;
  }

  // Verify the signature
  return verifier.verify(pemKey, decodedSignature);
}

// Express middleware
app.post('/webhooks/sendgrid', express.raw({ type: 'application/json' }), (req, res) => {
  const signature = req.get('X-Twilio-Email-Event-Webhook-Signature');
  const timestamp = req.get('X-Twilio-Email-Event-Webhook-Timestamp');

  if (!signature || !timestamp) {
    return res.status(400).send('Missing signature headers');
  }

  const publicKey = process.env.SENDGRID_WEBHOOK_VERIFICATION_KEY;
  const payload = req.body.toString();

  if (!verifySignature(publicKey, payload, signature, timestamp)) {
    return res.status(400).send('Invalid signature');
  }

  // Process events
  const events = JSON.parse(payload);
  console.log(`Received ${events.length} events`);

  res.sendStatus(200);
});

Using SendGrid SDK

const { EventWebhook } = require('@sendgrid/eventwebhook');

const verifyWebhook = new EventWebhook();
const publicKey = process.env.SENDGRID_WEBHOOK_VERIFICATION_KEY;

app.post('/webhooks/sendgrid', express.raw({ type: 'application/json' }), (req, res) => {
  const signature = req.get('X-Twilio-Email-Event-Webhook-Signature');
  const timestamp = req.get('X-Twilio-Email-Event-Webhook-Timestamp');

  const isValid = verifyWebhook.verifySignature(
    publicKey,
    req.body,
    signature,
    timestamp
  );

  if (!isValid) {
    return res.status(400).send('Invalid signature');
  }

  // Process webhook
  res.sendStatus(200);
});

Common Event Types

Event	Description	Use Cases
processed	Message has been received and is ready to be delivered	Track email processing
delivered	Message successfully delivered to recipient	Delivery confirmation
bounce	Message permanently rejected (includes type='blocked' for blocked messages)	Update contact lists, handle failures
deferred	Temporary delivery failure	Monitor delays
open	Recipient opened the email	Engagement tracking
click	Recipient clicked a link	Link tracking, CTR analysis
spam report	Email marked as spam	List hygiene, sender reputation
unsubscribe	Recipient unsubscribed	Update subscription status
group unsubscribe	Recipient unsubscribed from a group	Update group subscription preferences
group resubscribe	Recipient resubscribed to a group	Update group subscription preferences

Environment Variables

# Your SendGrid webhook verification key (public key)
SENDGRID_WEBHOOK_VERIFICATION_KEY="MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE..."

Local Development

For local webhook testing, use Hookdeck CLI:

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

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

Resources

• overview.md - What SendGrid webhooks are, common event types
• setup.md - Configure webhooks in SendGrid dashboard, get verification key
• verification.md - ECDSA signature verification details and gotchas
• examples/ - Complete implementations for Express, Next.js, and FastAPI

Related Skills

• webhook-handler-patterns - Cross-cutting patterns (idempotency, retries, framework guides)
• hookdeck-event-gateway - Webhook infrastructure that replaces your queue — guaranteed delivery, automatic retries, replay, rate limiting, and observability for your webhook handlers