await lettr.emails.send({
  from: 'you@example.com',
  to: ['recipient@example.com'],
  subject: 'Order Confirmation',
  html: '<p>Your order is confirmed!</p>',
  metadata: {
    orderId: 'order_12345',
    customerId: 'cust_67890',
    orderTotal: 99.99,
    source: 'checkout'
  }
});

{
  "type": "email.delivered",
  "data": {
    "emailId": "email_abc123",
    "to": "recipient@example.com",
    "metadata": {
      "orderId": "order_12345",
      "customerId": "cust_67890",
      "orderTotal": 99.99,
      "source": "checkout"
    }
  }
}

const emails = await lettr.emails.list({
  metadata: {
    orderId: 'order_12345'
  }
});

await lettr.emails.send({
  from: 'orders@example.com',
  to: ['customer@example.com'],
  subject: 'Order #12345 Confirmed',
  html: orderConfirmationHtml,
  
  // Tags for categorization
  tags: ['transactional', 'order-confirmation', 'us-region'],
  
  // Metadata for detailed tracking
  metadata: {
    orderId: 'order_12345',
    customerId: 'cust_67890',
    orderTotal: 299.99,
    currency: 'USD',
    itemCount: 3,
    shippingMethod: 'express',
    requestId: 'req_xyz789'
  }
});