Understanding Gmail and Apple Mail Email Prefetching: Implications for Open Tracking

In the realm of email marketing, open tracking is an essential tool for gauging the success of campaigns and understanding recipient engagement. However, recent developments in email client behavior, particularly within Gmail and Apple Mail, have introduced complexities that challenge the accuracy of email open tracking metrics. This article delves into the phenomenon of image prefetching and its impact on open tracking, shedding light on how these changes influence email marketing strategies.

Table of Contents

  1. Introduction
  2. Tracking Email Opens Using a Tracking Pixel
  3. Gmail Image Prefetching
  4. The Prefetching Process
  5. Apple Mail and Prefetching
  6. Anonymization of Recipient Data
  7. Mail Privacy Protection and its Reach
  8. Impact Beyond iCloud.com
  9. Unreliable Open Statistics
  10. Monitoring User-Agent Strings
  11. The Futility of Technical Workarounds
  12. Balancing Accuracy and Engagement Metrics
  13. Estimating Impact, Limitations, and Adaptation
  14. The Other Techniques to Track Email Engagement
  15. Conclusions

Tracking Email Opens Using a Tracking Pixel

Tracking email opens using a tracking pixel is a valuable and standard technique employed in email marketing campaigns. By embedding a tiny, invisible pixel within the email content, marketers can gather essential data on recipient behavior. When the email is opened, the pixel is loaded, sending a signal back to the sender's server. This action provides insights into the effectiveness of the email, including the open rate and the preferred timing of engagement. This data enables marketers to refine their strategies, optimize content, and tailor future campaigns for better reach and engagement. Overall, tracking email opens through the use of a tracking pixel enhances the ability to understand and connect with the target audience effectively.

Gmail Image Prefetching

Gmail, one of the most widely used email clients, employs image prefetching as part of its user experience optimization strategy. When a Gmail recipient is actively logged into the Gmail app, whether on the web or mobile version and receives an email while their session is ongoing, Gmail initiates the prefetching process. This process involves retrieving all images within the email just before the user interface displays the email. This action, commonly referred to as a "fake open", significantly influences tracking opens.

The Prefetching Process in Gmail

Prefetching occurs when the user is logged into Gmail and originates from a Google IP address. The request for prefetching is made using a specific user-agent string, which helps identify the Gmail application.

An example of this user-agent string is:

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.135 Safari/537.36 Edge/12.246 Mozilla/5.0  

This prefetching phenomenon is distinct from Google Image Cache opens, which take place when the user actually opens the email.

Apple Mail and Prefetching

Apple Mail introduces its own unique challenges to open tracking accuracy. Senders find it difficult to differentiate between genuine opens triggered by recipients using Apple Mail and those triggered by Apple's pre-fetching activities. This lack of differentiation renders open statistics unreliable.

Source:  https://www.apple.com/legal/privacy/data/en/mail-privacy-protection/  

Anonymization of Recipient Data

Apple employs a robust anonymization process for recipient data, encompassing IP addresses and user agents, as a core element of its comprehensive Mail Privacy Protection initiative. As a preliminary step before delivering subsequent message openings from its cache, this proactive measure ensures heightened user privacy. Consequently, any instances of repeated message openings within Apple Mail remain undisclosed to the original sender, adding a layer of confidentiality to recipient interactions. This deliberate anonymization procedure significantly heightens the intricacies involved in precisely tracking recipient interactions, thereby enhancing user privacy and challenging conventional recipient behavior monitoring techniques. This privacy-oriented approach reflects Apple's commitment to empowering users with greater control over their data and reshaping the landscape of digital communication privacy.

Mail Privacy Protection and its Reach

Mail Privacy Protection has far-reaching consequences that extend beyond the confines of specific email clients. Apple's innovative approach has a widespread impact, affecting not only individual email clients but also any email account integrated with the Apple Mail.app on iOS 15, iPadOS 15, or MacOS Monterey and later versions. This substantial change is anticipated to exert its influence across a significant proportion—approximately 20-40%—of the recipient's user base, marking a significant shift in how email privacy is upheld and reshaping the landscape of digital communication privacy.

Impact Beyond iCloud.com

The reach of Mail Privacy Protection extends beyond just iCloud.com. Its influence is felt even among those who predominantly rely on Gmail's web app or other email platforms. This impact becomes evident when configuring an email account within Apple Mail.app, triggering image prefetching regardless of whether the user engages with the application for actual email correspondence. This underscores how the implications of Mail Privacy Protection permeate various email ecosystems, showcasing its significance in enhancing user privacy across diverse email usage scenarios.

Monitoring User-Agent Strings

Effective monitoring of user-agent strings plays a pivotal role in comprehending the origins of email opens. Notably, Apple's proxy servers employ the distinctive user-agent string "Mozilla/5.0" when soliciting images, a characteristic marker that seems to reliably denote requests originating from these proxies. Vigilantly tracking any potential alterations to this string emerges as a critical task, ensuring precise segmentation and facilitating insightful analysis of user interactions.

Unreliable Open Statistics

Apple Mail and Gmail may display messages as opened even when the intended recipient has not interacted with the email. It's important to recognize that email service providers often utilize a practice wherein they store image content included in emails and serve them from their own servers. This discrepancy artificially inflates unique open statistics, which can mislead email marketers seeking accurate engagement data.

The Futility of Technical Workarounds

The history of attempting to bypass privacy safeguards using technical workarounds serves as a cautionary tale, highlighting their fleeting effectiveness and potential harm to sender’s reputation. It is crucial to bear in mind that the primary aim of email marketing is to captivate the intended audience. Embracing evolving, privacy-focused methods of gauging outcomes is not only prudent but also harmonizes perfectly with this overarching objective. This proactive approach not only respects users' privacy concerns but also nurtures genuine engagement and fosters long-lasting relationships with the target demographic.

Balancing Accuracy and Engagement Metrics

In addition to the aforementioned techniques for tracking email engagement, it's important to acknowledge a fundamental limitation: the inability to predict where an email will be opened. Since we can't anticipate the email client in which the message will be accessed (as this only occurs in the future), the open rate cannot a priori exclude user agents from the tracking events.

One potential approach could involve excluding certain user agents based on past opens, but this approach also has implications for open rates and unique open rates. By implementing such exclusions, a subset of users who genuinely engage with the email might be eliminated, leaving behind those who have never interacted with the mailing. This could skew the open rate metrics by affecting the ratio of opens to recipients, potentially leading to misleading interpretations of campaign success.

Estimating Impact, Limitations, and Adaptation

Google’s policy update has introduced a spectrum of effects on email open signal data, creating a variable impact that ranges from 0.5% to 10%, contingent upon the extent of Gmail utilization. For Apple Mail users this value may be even much higher – approximately 20-40% of total recipients, depending on the userbase. To effectively navigate this dynamic and ever-evolving scenario, email marketers must exhibit adeptness in recalibrating their strategies to align with the shifting behaviors of email clients. This entails not only an acute awareness of the changes but also a proactive approach to adapt and optimize recipient engagement.

In this intricate landscape, the emphasis on enhancing recipient engagement becomes paramount. Marketers need to delve deeper into understanding recipient behaviors, preferences, and interactions to cultivate meaningful connections. It is this concerted effort that fuels the transformation from a mere adaptation to a strategic advantage.

Synerise offers a comprehensive suite of complex Analytics tools that can be instrumental in addressing these challenges. Its sophisticated data analysis capabilities enable marketers to dissect the nuances of recipient interactions, glean insights into preferred email clients, and scrutinize the impact of Google's update on open rates. With Synerise, marketers can effectively track and measure the dynamic changes in engagement patterns, facilitating the adjustment of strategies and optimizing campaigns for better performance.

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Fig. 1: Synerise Analytics metric for excluding 'newsletter.open' events from User Agents used by Gmail in prefetching

The Other Techniques to Track Email Engagement

As the world of email marketing evolves, so do the methods for tracking recipient engagement. In addition to standard technique like tracking email opens using a tracking pixel, new challenges and opportunities arise with the advent of technologies like Gmail's image prefetching and Apple Mail's privacy measures. Navigating this intricate landscape requires a comprehensive understanding of these techniques and their implications. Synerise's solutions empower marketers to navigate this dynamic terrain with precision, foster genuine engagement, and build lasting connections with their target audiences:

  1. Link Click Tracking: This involves embedding unique tracking links within the email's content. When a recipient clicks on these links, the system records the interaction, allowing marketers to gauge interest and track click-through rates. If your email server provides such data, you can display it as events in Synerise CRM and further analyze it with our Analytics tools.
  2. UTM Parameters: Marketers can append UTM parameters to the URLs included in the email. These parameters help track the source, medium, and campaign that directed recipients to the website, providing insights into email-driven traffic. UTMs can be configured within communication tools in Synerise.
  3. Heatmaps and Analytics: Using specialized email marketing platforms like Synerise, marketers can generate heatmaps and detailed analytics reports that showcase recipient interactions, such as where they clicked, how far they scrolled, and which sections garnered the most attention.
  4. Segmented Analytics: By utilizing advanced analytics tools, also available in Synerise’s Analytics, marketers can analyze data based on specific segments of recipients, allowing for more targeted insights into different audience behaviors.
  5. Email Client Reporting: Some email service providers (SMTP) offer reports that show which email clients recipients are using to view emails. If you use such email provider, this data can be integrated into Synerise. This information can help optimize email designs for compatibility.
  6. Measuring Average Session Duration After Email Open or Click: Synerise allows you to track the average session duration on your website or mobile app following email opens and clicks. This valuable data can reveal the engagement levels of recipients after interacting with your email, aiding in the assessment of campaign effectiveness.
  7. Measuring Conversions: Synerise's comprehensive analytics tools enable marketers to measure conversions accurately. By tracking the actions taken by recipients after engaging with your email, such as completing a purchase or signing up for a service, you can gain insights into the direct impact of your email campaigns on driving desired outcomes.
  8. Identifying Re-engagement Opportunities: With Synerise, you can identify individuals who have not interacted with your website or mobile app recently but have shown engagement following email opens or clicks. This insight empowers you to design targeted re-engagement strategies, reactivating potentially dormant users and maximizing the impact of your email initiatives.


In this dynamic era of email client behaviors, particularly within platforms like Gmail and Apple Mail, email marketers find themselves navigating a landscape rife with both challenges and prospects. The advent of image prefetching has undoubtedly enhanced user experiences, yet concurrently introduced intricacies to open tracking techniques. As these transformations unfold, the key to sustained triumph lies in adeptly embracing the shifting landscape, emphasizing user engagement, and seamlessly integrating privacy-focused measurement methodologies. Amidst this paradigm, Synerise emerges as a potent ally, offering cutting-edge solutions that empower marketers to not only adapt but also flourish in an evolving email marketing ecosystem.