Why are email open tracking events not being registered for some recipients?
Matthew Whittaker
Co-founder & CTO, Suped
Published 21 Jul 2025
Updated 16 Aug 2025
8 min read
Email open tracking is a cornerstone metric for many marketers, offering a quick glance at engagement. However, it is increasingly common to encounter situations where open events are not registered for some recipients, even when you know they have read your emails or clicked on links. This discrepancy can be confusing and lead to misinterpretations of campaign performance.
The traditional method of tracking email opens relies on a tiny, often invisible, 1x1 pixel image embedded in the email. When an email client loads this image, it sends a request back to the server, which then registers an open event. This system, while widely adopted, has inherent limitations and is becoming less reliable due to evolving technology and privacy measures.
My goal is to explore the various reasons why open tracking events might not be registered, ranging from technical quirks to the broader privacy landscape. Understanding these factors is crucial for accurately assessing your email campaign performance and adapting your measurement strategies.
The technical fundamentals of open tracking
At its core, email open tracking operates by embedding a small, transparent image, often called a tracking pixel, into the HTML of an email. Each pixel is unique to the recipient and campaign. When the email is opened, the recipient’s email client or webmail service attempts to download all images, including this pixel. This download request is then logged by the sender’s email service provider (ESP) as an open event.
The immediate implication of this method is that if images are not loaded, an open cannot be registered. Many email clients, especially desktop versions or those with strict privacy settings, block images by default. Recipients must manually choose to display images for the pixel to fire. Furthermore, plain-text emails, by their nature, do not contain HTML and therefore cannot embed tracking pixels, meaning opens are never recorded for them. You can learn more about how email tracking pixels affect deliverability.
Another technical aspect to consider is the CNAME record used for tracking. Many email service providers (ESPs) require you to set up a custom tracking domain with a CNAME record that points to their servers. If this CNAME is not correctly configuredor resolving publicly, the tracking pixel won't load, and opens won't be recorded. This is a fundamental technical check to ensure your tracking infrastructure is operational.
The privacy landscape and its impact
The landscape of email privacy has significantly shifted, making open tracking increasingly unreliable. A major contributor to this is Apple Mail Privacy Protection (MPP), introduced with iOS 15. MPP pre-fetches and caches email content, including tracking pixels, through proxy servers, masking the user's IP address and actual open time. This means an email can be registered as opened even if the recipient never actually viewed it.
For some recipients, particularly those using Apple Mail, this can lead to artificially inflated open rates. Conversely, for others, genuine opens might not be registered. This is because MPP can also interfere with the traditional pixel firing mechanism, making it difficult to distinguish between a genuine user open and a pre-fetch by Apple’s servers. Read more about how Gmail's image proxy affects open tracking.
Beyond MPP, many users employ ad blockers, browser extensions, or VPNs that specifically target and block tracking pixels or prevent images from loading by default. If these tools are active, the tracking pixel will never be downloaded, and thus, no open event will be recorded. This is a common reason for legitimate opens going unregistered, especially among tech-savvy users or those highly conscious of their privacy. Some email clients or browsers block images for this reason.
Deliverability and reputation nuances
While open tracking primarily depends on image loading, deliverability can indirectly influence whether opens are registered. If your emails are consistently landing in spam folders or being blocked outright, recipients won't even see them, let alone open them. Even if they reach the inbox, an email that triggers spam filters might have its images stripped or blocked by the email client, preventing the pixel from firing. This is why emails going to spam can impact perceived open rates.
Your sender reputation plays a significant role here. A poor reputation can lead to more aggressive filtering by Internet Service Providers (ISPs), affecting overall email deliverability and potentially the loading of tracking pixels. If your domain or IP address lands on a blocklist (or blacklist), emails may not even reach the inbox, making open tracking impossible. It is worth investigating if your domain is on an email blacklist.
I’ve seen instances where the choice of subdomain itself can impact open tracking. Some subdomains might be flagged by ad-blocking extensions or corporate firewalls due to their naming convention or association with past problematic sending. If you're testing with different subdomains and seeing varied open rates, it could indicate a reputation issue specific to that subdomain, causing images (and thus pixels) to be blocked. This is distinct from general deliverability, as the email might reach the inbox, but the tracking component is suppressed.
It’s important to remember that some ISPs and email clients, like Gmail, also use image proxying, which can mask the true open status. While this isn't necessarily a deliverability problem in terms of reaching the inbox, it fundamentally alters how open events are recorded and complicates their interpretation. This is why email open rates are mostly dead as a reliable metric.
Technical issues with your tracking system
Traditional open tracking
Method: Relies on a 1x1 tracking pixel loading when an email is opened.
Accuracy: Highly susceptible to image blocking, privacy features, and pre-fetching.
Limitations: Doesn't account for true engagement beyond pixel load, often misleading.
Focus on engaged metrics
Better Metrics: Track clicks, conversions, replies, and time spent in the email.
Accuracy: Provides a more reliable indication of recipient interest and action.
Benefits: Guides better content and targeting strategies, improving ROI.
The primary cause for unrecorded open events, despite an email being opened, can often be traced back to the tracking system itself. Many ESPs, even reputable ones like SendGrid, process open pixel loads. This processing might involve filtering out automated opens (like those from security scanners or Apple MPP pre-fetching) before reporting them to you. While this aims to provide cleaner data, it can also lead to legitimate opens being intentionally excluded.
Another technical issue could be related to your domain's DNS configuration. If your tracking CNAME record is incorrect, expired, or experiencing resolution issues, the pixel cannot be reached, and no open will be recorded. This is a crucial check, especially if you've recently made changes to your DNS or migrated ESPs.
Finally, the inconsistencies you observe with different email clients or subdomains highlight the inherent unreliability of open tracking. Mobile apps, desktop clients, and webmail interfaces handle image loading differently. A mobile app might not load images by default, while a desktop client might, leading to disparate tracking results for the same recipient depending on how they view the email. This is why it’s becoming increasingly important to explore alternative email tracking mechanisms.
Views from the trenches
Best practices
Don't rely solely on open rates, focus on clicks and conversions for true engagement.
Implement robust email authentication like SPF, DKIM, and DMARC for better deliverability.
Regularly clean your email lists to remove inactive or invalid addresses, improving list health.
Segment your audience and personalize content to drive higher interaction beyond just opens.
Common pitfalls
Ignoring the impact of Apple Mail Privacy Protection on reported open metrics.
Not verifying your tracking CNAME records are correctly configured and publicly resolving.
Attributing all low open rates to deliverability issues without investigating tracking setup problems.
Using subdomains that might trigger ad-blocking extensions or corporate network filters.
Expert tips
Test your open tracking pixel independently by fetching it directly and checking your logs.
Analyze engagement beyond opens, such as click-through rates and replies, for more accurate insights.
Monitor your DMARC reports for authentication failures, which can indirectly affect inbox placement.
Consider using different sending subdomains for various email types or markets to isolate issues.
Marketer view
Marketer from Email Geeks says they've experienced similar problems with open-tracking events not being registered, especially on specific devices or applications, leading to a decrease in their newsletter's open rate.
2023-04-13 - Email Geeks
Expert view
Expert from Email Geeks says that the described pattern sounds like a problem with the tracking system itself rather than purely an email deliverability issue. They suggest generating links and using tools like wget or curl to fetch them, then verify if the opens are correctly recorded by the tracking system.
2023-04-13 - Email Geeks
Navigating unreliable open rates
The challenges in accurately tracking email opens are growing, driven by a combination of evolving privacy features, strict email client behaviors, and potential technical misconfigurations. It's clear that relying solely on open rates can lead to a skewed understanding of your email campaign performance.
To gain a more precise picture of engagement, I encourage a shift in focus from opens to more tangible metrics such as click-through rates, conversions, and replies. These actions unequivocally indicate that a recipient has interacted with your content. You can also explore methods for accurately measuring open rates without pixels.
By understanding the complexities behind why open events might not be registered, and by adjusting your measurement approach, you can still gain valuable insights into your audience's behavior and optimize your email marketing strategies effectively.
SendGrid, process open pixel loads. This processing might involve filtering out automated opens (like those from security scanners or Apple MPP pre-fetching) before reporting them to you. While this aims to provide cleaner data, it can also lead to legitimate opens being intentionally excluded.
