Cross-Device Tracking via Email Hash

• All links in marketing emails should include the ehash parameter in the URL.

• All email addresses captured onsite (e.g., during checkout or signup) must be hashed client-side and sent to GA4 as event parameters.

• Generate a hash (e.g., using SHA-256).

• Store it in your backend.

• Include the hashed email as a query parameter in all email links:

plain text
https://www.example.com/landing-page?ehash=hashedemail123

1. Create Variable
1. Go to Variables in GTM.
2. Click New > Choose Variable Type: URL.
3. Set Component Type to Query.
4. In Query Key, enter: ehash.
5. Name it something like Query - ehash.
This variable will now dynamically grab ehash from the URL if it exists.

2. Pass it as an Event Parameter to the GA4 Google Tag
1. Select your GA4 initialisation Google Tag.
2. Open the Shared event settings section and create or edit the Event Settings Variable.
3. Inside the variable set the event parameter name to ehash and the value to {{Query - ehash}}.
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This will ensure the ehash parameter is passed to GA4 when there is a ehash parameter in the URL, and SegmentStream will automatically match different devices when they are tracked with the same ehash.

1. Ask your developers to push an event into the dataLayer that includes the ehash value whenever a form with an email is submitted, or add the ehash parameter to existing dataLayer events that are already sent on form submission, for example:

javascript
dataLayer.push({
  event: "email_form_submitted",
  ehash: "<user email hashed using the method as in the email links>"
});

2. Inside your GTM, create a Data Layer Variable for ehash
1. Go to Variables → New
2. Name: DLV – ehash
3. Type: Data Layer Variable
4. Data Layer Variable Name: ehash
5. Your variable should look like this:
6. Save

3. If the dataLayer event is already tracked, skip this step, else, create a GTM Trigger for the event, in our example it’s email_form_submitted.
1. Go to Triggers → New
2. Name: Trigger – email_form_submitted
3. Trigger Type: Custom Event
4. Event name: email_form_submitted
5. Your trigger should look like this:
6. Save

4. If the event is already tracked in GA4, skip this step, else, create a GA4 tag to send the event.
1. Go to Tags → New
2. Name: GA4 – email_form_submitted
3. Tag Type: Google Analytics: GA4 Event
4. Configuration Tag: Select your existing GA4 config tag
5. Event Name: email_form_submitted
6. Triggering: Trigger – email_form_submitted

5. In the event that is tracking the form submission, edit the Event Parameters to add the following:
• Name: ehash
• Value: {{DLV – ehash}}

6. Your tag should look like this:

7. Save and publish the container

1. Ask your developers to include the ehash parameter in the purchase event pushed to the dataLayer when a transaction is completed and the user’s email is available.

javascript
dataLayer.push({
  event: "purchase",
  ehash: "<user email hashed using the method as in the email links>"
  ecommerce: {
    transaction_id: "T12345",
    value: 59.99,
    currency: "USD",
    items: [
      {
        item_id: "SKU_123",
        item_name: "Wireless Mouse",
        price: 29.99,
        quantity: 2
      }
    ]
  }
});

2. Inside your GTM create a Data Layer Variable for ehash
1. Go to Variables → New
2. Name: DLV – ehash
3. Type: Data Layer Variable
4. Data Layer Variable Name: ehash
5. Your variable should look like this:
6. Save.

3. Open the GA4 Tag that is tracking the purchase event and edit the Event Parameters to add the following:
• Name: ehash
• Value: {{DLV – ehash}}

4. Your tag should look like this:

5. Save and publish the container.