Summary
Prefetch and proxy opens represent significant complexities in accurately tracking email engagement. While often confused, they describe distinct mechanisms that impact how and when an email open is registered. Prefetching refers to automated image loading by email clients or servers before a user actually views the email. Proxying, on the other hand, involves routing image requests through an intermediary server, obscuring the original user's IP address and device details. Both can lead to inflated or misleading open rates, making it challenging for marketers to interpret engagement metrics accurately.
Key findings
- Distinct processes: Prefetching happens as an email is delivered or built for display, often before a user opens it, while proxying involves routing image requests through an intermediary server.
- Data obfuscation: Proxy opens mask the user's true location and device details, as the IP address fetching the image belongs to the proxy, not the end user.
- Non-human interaction (NHI): Prefetched opens are typically a form of NHI, where automation, not direct user action, triggers the image load. This means an email open might not reflect actual engagement.
- Inflated metrics: Both mechanisms can lead to inflated open rates, as images are loaded without a human viewing the email, thus providing unreliable data for performance measurement.
- Apple mail privacy protection (MPP): Apple's Mail Privacy Protection is a prominent example of a system that combines both prefetching and proxying to enhance user privacy.
Key considerations
- Reliance on clicks: Given the unreliability of open rates, focusing on unique click-through rates (CTR) can provide a more accurate measure of user engagement.
- Data noise: Email open rate data is increasingly noisy, making it difficult to discern actual recipient behavior changes from technical anomalies.
- Provider-specific analysis: Analyzing open rates by mailbox provider (e.g., Gmail, Apple Mail) can help identify if drops are due to specific technical changes by a provider or broader deliverability issues, as discussed by Mailmodo regarding Gmail prefetching.
- Beyond open rates: Marketers should shift focus to other metrics like clicks, conversions, and subscriber retention to truly gauge campaign performance.
What email marketers say
Email marketers frequently grapple with the implications of prefetch and proxy opens on their campaign analytics. Many express frustration over the diminishing reliability of open rates as a key performance indicator. They are increasingly looking for alternative metrics that provide clearer insights into user engagement, acknowledging that the traditional 'open' metric no longer solely reflects human interaction. The shift towards privacy-enhancing features by major email clients (like Apple Mail) has accelerated this re-evaluation, pushing marketers to adapt their measurement strategies.
Key opinions
- Confusion between terms: There's often uncertainty about whether prefetch and proxy opens are synonymous or distinct concepts among marketers.
- Inflated open rates: Many marketers recognize that these automated opens contribute to inflated open rates, making the data less reliable for measuring true subscriber interest.
- Impact on campaign analysis: The inaccuracies introduced by prefetch and proxy opens complicate campaign performance analysis, forcing a re-evaluation of how success is defined.
- Shift to other metrics: Marketers are increasingly looking to click rates and conversions as more meaningful indicators of engagement.
Key considerations
- Adapting measurement: It's crucial for marketers to adapt their measurement strategies to account for the impact of prefetch and proxy opens, reducing reliance on raw open rates.
- Focus on unique clicks: If unique click rates remain consistent despite a drop in opens, it likely indicates a change in how opens are being tracked, not a true decline in interest, as highlighted by Trust Insights.
- Segmenting by provider: Breaking down open rate changes by email service provider (ESP) or mailbox provider can help identify specific issues, like a shift to a Gmail promotions tab or a proxy glitch from Apple.
- Monitoring ESP reports: Marketers need to be aware that ESP reporting methods for opens can change, causing sudden shifts in reported metrics.
Marketer view
Email marketer from Email Geeks defines prefetch opens as those that occur when the email is being delivered, not necessarily when the end user opens it. Proxy opens, on the other hand, mask the user's device and location details, and can happen either during prefetch or when the user actually opens the email. Typically, both types of opens are proxied, meaning their true origin is obscured.
Marketer view
Email marketer from Email Geeks inquired about the relationship between prefetch opens and proxy opens, seeking clarification on whether they are the same. This highlights a common point of confusion for those trying to accurately interpret email performance data.
What the experts say
Email deliverability experts provide critical distinctions between prefetch and proxy opens, emphasizing that 'open' data is increasingly unreliable due to automated processes and privacy features. They stress that an open only signifies an image fetch, which may or may not be triggered by human interaction. Experts advise a more nuanced approach to data interpretation, suggesting a focus on supplementary metrics and granular analysis by mailbox provider to gain a clearer picture of email performance.
Key opinions
- Opens are image fetches: Experts clarify that an 'open' fundamentally means an image (tracking pixel) was fetched, regardless of who or what initiated the request.
- Non-human interaction (NHI) opens: NHI opens occur when automation, not a human, fetches the image, often prior to the user even seeing the email, creating significant uncertainty about actual viewing.
- Proxy impact: Proxies hide user IP addresses and client details, making it impossible to determine the true source of an open or use traditional tracking methods.
- No simple answer: Prefetch and proxy opens are not the same; an open can be either, both, or neither, adding layers of complexity to open rate interpretation.
- Data is noisy: The current email ecosystem generates very noisy open data, making it hard to interpret ESP reports accurately without deeper investigation.
Key considerations
- Analyze by mailbox provider: A crucial step in diagnosing open rate fluctuations is to break down the data by mailbox provider, as specific changes (e.g., Gmail's image proxy) can heavily influence results.
- Look for specific causes: Sudden drops might indicate a change in a mailbox provider's prefetching behavior or proxy glitches, rather than a genuine decline in subscriber engagement.
- Don't panic over open rate drops alone: If unique click rates remain stable despite falling open rates, it's generally not a cause for panic, but still warrants investigation to understand the underlying technical changes. This is echoed in our guide on why deliverability rates can be wrong.
- Understand the limitations: It's vital for deliverability professionals and marketers to understand the inherent limitations of open rate data in the current email landscape.
Expert view
Expert from Email Geeks explains that pre-fetch occurs when an email client builds the message for display, happening between delivery and the user viewing the message. This pre-fetching can occur multiple times, especially for users accessing emails across different devices, adding complexity to open tracking.
Expert view
Expert from Email Geeks defines proxies as mechanisms that conceal the individual location and potentially device details of a user. For example, Apple image loads are routed through the Apple proxy network, and mobile phone opens often appear from network servers rather than the specific user's location.
What the documentation says
Technical documentation and research shed light on the underlying mechanisms of prefetch and proxy operations, explaining how they function to optimize performance and enhance user privacy. These resources often delve into the specifics of how email clients and internet service providers implement these features, detailing the implications for tracking pixels and IP address visibility. Understanding these technical foundations is crucial for grasping why traditional email open metrics have become less reliable and for developing more accurate measurement strategies.
Key findings
- Image fetching: Email opens are fundamentally tied to the fetching of small, embedded images (tracking pixels) within the email content.
- Client-side prefetching: Some email clients are designed to prefetch images to ensure emails load quickly and seamlessly when a user eventually opens them, regardless of user interaction.
- Proxy server function: Proxy servers act as intermediaries, retrieving content on behalf of the end-user. This design means the server's IP address is recorded, not the user's, for privacy and performance reasons, as explained by Sitelint regarding caching proxies.
- Privacy implications: Proxying is a key component of privacy features (e.g., Apple MPP), preventing senders from gathering precise user data like location or device types.
Key considerations
- Understanding MIME types: The loading of email content, including tracking pixels, relies on HTTP requests and MIME types for proper rendering, which can be affected by proxying.
- Caching behavior: Prefetched images are often cached. This means subsequent actual opens by the user might not trigger a new image request, further complicating accurate tracking.
- Protocol-level tricks: Proxying aims to eliminate traditional protocol-level tracking methods that could link users across different websites and email senders.
- User-agent strings: With proxy opens, the user-agent string reflects the proxy's system, not the end user's device or email client, limiting insights into recipient environment.
Technical article
Documentation from MDN Web Docs clarifies that a Media Type, formerly known as a Multipurpose Internet Mail Extensions (MIME) type, is essential for indicating the nature and format of a document or file. In email, this ensures images and other content are rendered correctly, and understanding MIME types is fundamental to how tracking pixels (images) are fetched.
Technical article
Documentation from Mailmodo.com specifically outlines that Gmail prefetching causes an inflated open rate under various circumstances, leading to unreliable and misleading metrics. This highlights how a major email provider's technical implementation directly impacts sender analytics.
Related resources
6 resources
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