To achieve a holistic view of the user journey, it’s essential to capture engagement signals from Email and SMS campaigns—such as opens, clicks, and conversions. While client-side tracking is often blocked by privacy settings and app environments, server-side tracking ensures reliability, better attribution, and GDPR/CMP compatibility.

✅ Why Server-Side for Email/SMS?

• ✅ Avoids tracking being blocked by email clients or privacy features
• ✅ Captures user actions even in AMP or native mobile environments
• ✅ Maintains tracking across device sessions
• ✅ Complies with consent & privacy regulations
• ✅ Links clicks and conversions to campaign IDs reliably

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🔧 Prerequisites

• Server-Side GTM container set up (https://gtm.yourdomain.com)
• Web GTM container installed on site
• Email & SMS platform that supports:
  • Open pixel injection
  • Click tracking URLs
• GA4 property + Measurement Protocol API Secret
• Consent Management Platform (CMP), optional but recommended

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🚀 Step-by-Step Implementation

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🔹 Step 1: Email Open Tracking via Server Pixel

Concept: Inject a 1×1 pixel in the email HTML that points to a Server-Side GTM endpoint.

Pixel URL:

https://gtm.yourdomain.com/collect?event=email_open&email_id=abc123&campaign=summer25

Email HTML Example:

<img src="https://gtm.yourdomain.com/collect?event=email_open&email_id={{user_id}}&campaign={{campaign_name}}" width="1" height="1" style="display:none;">

✅ This request will trigger the GA4 Client in your ssGTM container.

🔹 Step 2: Server-Side GTM: Capture Email Opens

Create a GA4 Client (if not already done)

Create a Custom Trigger in Server-Side GTM:

• Condition: event_name equals email_open

GA4 Event Tag in ssGTM:

• Event Name: email_open
• User Properties:
  • email_id: {{Query - email_id}}
  • campaign: {{Query - campaign}}

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🔹 Step 3: SMS Click Tracking via Redirect URL

SMS links should route through your server container:

Shortened Link Format:

https://gtm.yourdomain.com/sms-click?user_id=abc123&campaign=promo01&redirect=https%3A%2F%2Fyourdomain.com%2Foffer

Click Handler Setup in Server GTM:

1. Create a Custom Client (type: HTTP)
2. Parse URL params:
   • user_id
   • campaign
   • redirect
3. Fire a GA4 Event Tag:
   • Event Name: sms_click
   • User Properties: user_id, campaign
4. Redirect user using a Response Header Variable:

return {
  statusCode: 302,
  headers: {
    'Location': decodeURIComponent(request.query.redirect)
  }
}

🔹 Step 4: Correlate Conversions with Email/SMS Campaigns

When the user lands on your site and eventually converts, pass the same user_id and campaign stored in cookies or session.

Store data from pixel click:

// On landing page
const urlParams = new URLSearchParams(window.location.search);
const userId = urlParams.get('user_id');
const campaign = urlParams.get('campaign');

if (userId && campaign) {
  document.cookie = `email_user=${userId}; path=/; max-age=2592000`;
  document.cookie = `email_campaign=${campaign}; path=/; max-age=2592000`;
}

🔹 Step 5: Push Data to dataLayer for Web GTM

<script>
const getCookie = (name) => {
  const match = document.cookie.match(new RegExp('(^| )' + name + '=([^;]+)'));
  return match ? decodeURIComponent(match[2]) : null;
};

dataLayer.push({
  event: 'email_sms_attribution',
  email_user: getCookie('email_user'),
  email_campaign: getCookie('email_campaign')
});
</script>

🔹 Step 6: Include Attribution Data in Conversions

Update your GA4 purchase/lead tag in Web GTM:

Parameters:

• email_user: {{DLV - email_user}}
• email_campaign: {{DLV - email_campaign}}

If using Server-Side GTM, ensure you forward these fields as parameters to your server GA4 tag.

✅ Use GA4 Custom Dimensions to persist email_campaign

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🔹 Step 7: Reporting in GA4

Create Custom Dimensions for:

• email_campaign
• sms_campaign
• user_id (hashed or UUID)

Then build Explorations:

• Campaign → Clicks → Purchases
• Users by campaign over time
• Email open vs conversion rate

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🔹 Step 8: Consent Mode & Privacy Handling

Ensure no tracking fires until consent is granted.

In GTM:

gtag('consent', 'default', {
  ad_storage: 'denied',
  analytics_storage: 'denied'
});

Use Consent Triggers in both Web and Server containers.

🔹 Step 9: Debugging Tips

• Use GTM Server-Side Preview to see pixel and redirect hits
• Check /collect?event=email_open payloads
• Log redirected SMS click URL activity
• Validate GA4 Realtime → filter by email_campaign
• Use Looker Studio for aggregated attribution reports

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🔐 Security Notes

• Sanitize incoming query params on ssGTM endpoint
• Avoid exposing raw emails—use hashed email_id (e.g., SHA-256)
• Ensure redirect URLs are validated to prevent open redirects

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🧠 Summary

Step	Action
1	Use open tracking pixels for email
2	Set up GA4 event for email_open
3	Redirect and log SMS clicks via ssGTM
4	Store user/campaign IDs in cookies
5	Push attribution into GA4 conversion events
6	Use custom dimensions for campaign attribution
7	Implement consent-aware triggers
8	QA via GTM debug & GA4 DebugView