Email open tracking has long been a common requirement in digital analytics. In Universal Analytics (GA3), this was typically implemented using the Measurement Protocol, where a simple HTTP request would be triggered when an email was opened.
With the transition to GA4, the Measurement Protocol has become more structured and strict. While this improves data consistency and governance, it also increases implementation complexity—especially for lightweight scenarios like email open tracking.
However, in practice, there is still a way to achieve a GA3-like implementation using GA4’s request mechanism.
Understanding the GA4 Request Flow
To understand how GA4 receives data, you can inspect network requests using browser developer tools.
Filter requests with “v=2”
These requests represent data being sent to GA4 in real time.
Although the full request payload may appear long and complex, most parameters are not necessary for basic event tracking scenarios such as email opens.
What We Actually Need from the Request
For a simplified email tracking implementation, only a few core fields are important.
- cid: This is the identifier used by GA4 to associate the event with a user or device. It must be dynamically replaced with the recipient’s actual Client ID. Without it, GA4 cannot properly attribute the event
- en: event name, this defines the event being recorded in GA4.
- ep: event parameter, these are optional event attributes.
How Email Open Tracking Works
The core idea is to embed a hidden tracking request inside the email using an image tag.
The final effect is that the img cannot be seen in the email:
Send the email, and when a user opens it, a request is sent to GA4’s collect endpoint, the event appears in GA4 Real-time reports
Summary
GA4’s Measurement Protocol is more structured than GA3, but the core idea behind email open tracking remains the same.
By leveraging a simple collect request embedded in an invisible image, and focusing on three key fields:
cid(Client ID)en(Event name)ep(Event parameters)
You can still implement a GA3-style email open tracking mechanism within GA4.
This approach is lightweight, practical, and suitable for basic email engagement measurement scenarios.
