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Beta Feature: Open tracking is currently in beta and available on paid plans only. Features and behavior may change before general availability.

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How It Works

When open tracking is enabled for a route, Lettermint automatically injects a transparent 1x1 tracking pixel into your HTML emails. The pixel is inserted just before the closing </body> tag. 
<!-- Your email content -->
<img src="https://t.ltrmnt.com/o/{tracking_token}"
     width="1" height="1"
     style="display:block;width:1px;height:1px;border:0;"
     alt="">
</body>
When the recipient’s email client renders the email and loads images, the pixel request is recorded as an open event.

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Enabling Open Tracking

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Via Dashboard

  1. Navigate to your project
  2. Go to Routes and select your transactional or broadcast route
  3. In Route Settings, enable Track Opens
  4. Save your changes

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Via API

curl -X PATCH https://api.lettermint.co/v1/routes/{route_id} \
  -H "Authorization: Bearer {team_api_token}" \
  -H "Content-Type: application/json" \
  -d '{"track_opens": true}'
Open tracking is only available for transactional and broadcast routes. Inbound routes cannot have tracking enabled.

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Bot Detection

Many email opens are not from actual humans viewing the email. Email clients, security tools, and privacy features can trigger open events automatically. Lettermint detects these automated interactions to give you accurate engagement data.

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Webhook Payload

When an open is detected, Lettermint sends a message.opened webhook event: 
{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "event": "message.opened",
  "timestamp": "2025-08-08T20:17:00.000Z",
  "data": {
    "message_id": "f47ac10b-58cc-4372-a567-0e02b2c3d479",
    "subject": "Your order has shipped",
    "metadata": {
      "X-Order-ID": "order-12345"
    },
    "tag": "shipping",
    "recipient": "[email protected]",
    "opened_at": "2025-08-08T20:17:00+00:00",
    "first_open": true,
    "device_type": "desktop",
    "client_type": "browser",
    "client_name": "Chrome",
    "user_agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)...",
    "bot": {
      "detected": false,
      "probability": 5
    }
  }
}
Engagement fields:
  • first_open - true if this is the first time this recipient opened the email
  • device_type - Device category: desktop, mobile, or tablet
  • client_type - Client category: browser, email_client, etc.
  • client_name - Specific client name: Chrome, Safari, Outlook, etc.
Bot detection fields:
  • bot.detected - true if the open appears automated
  • bot.probability - Confidence score from 0-100 (higher = more likely a bot)

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Limitations

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HTML Emails Only

Open tracking requires HTML content. The tracking pixel cannot be added to:
  • Plain-text only emails
  • Emails where the recipient views only the text part

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Token Expiration

Tracking tokens expire 30 days after the email is sent. Opens after this period are not recorded. This protects recipient privacy and reduces long-term data storage.

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Privacy Proxies

Some email clients pre-fetch images to protect user privacy:
  • Apple Mail Privacy Protection - Loads all images automatically, regardless of whether the user opens the email
  • Hey Email - Similar privacy-first image loading
  • ProtonMail - Images loaded through proxy servers
While Lettermint detects most proxy traffic, these features can inflate open rates. Use bot detection fields to filter your analytics.

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Image Blocking

Some recipients configure their email clients to block images by default. These opens will only be recorded if the recipient explicitly loads images.

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Best Practices

  1. Don’t rely solely on opens - Click tracking provides stronger engagement signals
  2. Consider privacy - Be transparent with recipients about tracking in your privacy policy
  3. Monitor trends - Individual open rates vary; focus on aggregate trends over time

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Next Steps