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Overview

Open Tracking

1x1 invisible pixel tracks when emails are opened

Click Tracking

Links are rewritten to track clicks before redirecting

Analytics

View open/click rates in dashboard or via API

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How It Works

When you send an email with tracking enabled:
  1. A transparent 1x1 pixel image is added to track opens
  2. All links in the email are rewritten through our tracking servers
  3. When the recipient opens the email or clicks a link, we record the event
  4. Events trigger webhooks and are available via the Events API

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Open Tracking Pixel

GET/v1/track/open/:emailId
This endpoint serves a 1x1 transparent GIF pixel and records an open event for the email. It’s automatically embedded in emails when open tracking is enabled.

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Behavior

  • Records the first open with timestamp in the opened_at field
  • Creates an email_event record with type opened
  • Captures user agent and IP address metadata
  • Triggers email.opened webhook if configured
  • Always returns a 1x1 transparent GIF with no-cache headers
Pixel URL
<img src="https://www.unosend.co/api/v1/track/open/550e8400-e29b-41d4-a716-446655440000" 
     width="1" height="1" alt="" style="display:none" />

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Response Headers

Content-Type: image/gif
Cache-Control: no-store, no-cache, must-revalidate, proxy-revalidate
Pragma: no-cache
Expires: 0
Open tracking relies on image loading, which can be blocked by some email clients. Open rates should be considered a lower-bound estimate.

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Click Tracking Redirect

GET/v1/track/click/:trackingId
This endpoint records a click event and redirects the user to the original URL. Links are automatically rewritten when click tracking is enabled.

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Query Parameters

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url
string
URL-encoded destination (for broadcast mode)
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tid
string
Optional tracking identifier

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Behavior

  • Looks up original URL from the tracking ID or uses the url query param
  • Creates an email_event record with type clicked
  • Captures user agent, IP address, and referer metadata
  • Triggers email.clicked webhook if configured
  • Returns 302 redirect to the original destination URL
Tracked Link Example
<!-- Original link -->
<a href="https://example.com/page">Click here</a>

<!-- Becomes -->
<a href="https://www.unosend.co/api/v1/track/click/abc123?url=https%3A%2F%2Fexample.com%2Fpage">Click here</a>

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Response

HTTP/1.1 302 Found
Location: https://example.com/page

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Enable Tracking When Sending

To enable tracking, include the tracking options when sending an email: 
curl -X POST https://www.unosend.co/api/v1/emails \
  -H "Authorization: Bearer un_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "[email protected]",
    "to": "[email protected]",
    "subject": "Hello",
    "html": "<p>Check out <a href=\"https://example.com\">our site</a>!</p>",
    "tracking": {
      "open": true,
      "click": true
    }
  }'
You can enable open tracking and click tracking independently based on your needs.

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Webhook Events

When opens or clicks are tracked, webhooks are triggered:

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email.opened

email.opened webhook
{
  "type": "email.opened",
  "data": {
    "email_id": "550e8400-e29b-41d4-a716-446655440000",
    "opened_at": "2024-01-15T10:45:00.000Z",
    "user_agent": "Mozilla/5.0...",
    "ip_address": "192.168.1.1"
  },
  "created_at": "2024-01-15T10:45:00.000Z"
}

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email.clicked

email.clicked webhook
{
  "type": "email.clicked",
  "data": {
    "email_id": "550e8400-e29b-41d4-a716-446655440000",
    "url": "https://example.com/page",
    "clicked_at": "2024-01-15T10:47:00.000Z",
    "user_agent": "Mozilla/5.0...",
    "ip_address": "192.168.1.1"
  },
  "created_at": "2024-01-15T10:47:00.000Z"
}
IP addresses and user agents are collected for analytics. Make sure your privacy policy reflects this if you’re using tracking features.

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Controlling Tracking

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Via API

Use the tracking object to enable or disable open and click tracking per email: 
{
  "from": "[email protected]",
  "to": ["[email protected]"],
  "subject": "Hello",
  "html": "<p>Check out <a href=\"https://example.com\">our site</a>!</p>",
  "tracking": {
    "open": true,
    "click": false
  }
}
OptionDefaultDescription
tracking.opentrueEnable open tracking (invisible pixel)
tracking.clicktrueEnable click tracking (link rewriting)

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Via SMTP Headers

When using SMTP, add custom headers to control tracking: 
X-Unosend-Track-Opens: true
X-Unosend-Track-Clicks: false
Example with SMTP: 
From: [email protected]
To: [email protected]
Subject: Hello
X-Unosend-Track-Opens: true
X-Unosend-Track-Clicks: false
Content-Type: text/html

<p>Hello!</p>
Set tracking.click to false if you don’t want links rewritten. This keeps original URLs intact, which can improve deliverability to some security-conscious recipients.