What methods do ESPs and SMTP providers use to identify Apple MPP and GoogleProxyImages?
Matthew Whittaker
Co-founder & CTO, Suped
Published 30 Aug 2025
Updated 10 Sep 2025
6 min read
The introduction of Apple Mail Privacy Protection (MPP) and Google Proxy Images has significantly altered how email service providers (ESPs) and SMTP providers track email engagement. These privacy measures pre-fetch images, including tracking pixels, making it challenging to distinguish between an actual user open and a machine-generated one. This has led to inflated open rates and a need for more sophisticated identification methods.
For email marketers and deliverability specialists, understanding how these proxy opens are identified is crucial for accurate analytics and maintaining effective strategies. The core challenge lies in the intended obfuscation of user activity. However, ESPs and SMTP providers employ various technical signals and heuristics to categorize these interactions.
How Apple Mail Privacy Protection (MPP) works
Apple Mail Privacy Protection (MPP), launched with iOS 15, iPadOS 15, and macOS Monterey, is designed to prevent email senders from learning a recipient's IP address and whether they have opened an email. It achieves this by routing all email image loads through a proxy server. When an email arrives in an Apple Mail inbox, even if the user hasn't explicitly opened it, Apple's servers pre-fetch all images, including tracking pixels. This means every email sent to an Apple Mail user with MPP enabled appears as an open.
The primary impact for ESPs is the unreliability of traditional open rate metrics. What looks like a 100% open rate might actually be a mix of legitimate user engagement and automated proxy opens. This makes it difficult to gauge campaign performance or segment users based on their engagement behavior.
To address this, ESPs have had to adapt their tracking methods. For a detailed understanding of how MPP affects tracking, see our article on Apple Mail Privacy Protection and open tracking.
Key characteristics of Apple MPP opens
IP address masking: All image requests appear to come from Apple's proxy servers, hiding the recipient's true location and device.
Automated pre-fetching: Images are downloaded upon email receipt, not necessarily when the user opens the email.
Generic user agent: Often a standard Mozilla/5.0 string, making it less distinct for identification.
Identification methods for proxy opens
ESPs and SMTP providers leverage a combination of signals to differentiate between real and proxy opens. While no single method is foolproof due to the privacy enhancements, combining multiple data points helps in making an educated guess.
IP address and ASN: Apple publishes the IP ranges of its proxy servers. If an open request originates from one of these known IP addresses or Autonomous System Numbers (ASN), it is a strong indicator of an MPP open. This is a primary method for many ESPs.
User-Agent string: While some initially reported a unique user agent for MPP, it often appears as a generic Mozilla/5.0. However, the combination of this generic user-agent with an Apple IP can still be a strong signal. Yahoo's documentation also outlines how they handle proxy servers for their mail. Surprisingly, Apple, Google, and Yahoo have not randomized the user agent string, simplifying this aspect.
Timing of open: MPP and other proxy services often trigger an image load within seconds or minutes of an email being delivered. ESPs can use this rapid open timestamp as a heuristic to flag potential proxy opens. Removing opens that occur within a very short window (e.g., 2-3 minutes) of delivery is a common approach.
rDNS (Reverse DNS): Examining the reverse DNS lookup of the IP address can sometimes reveal if it belongs to a known proxy or data center, rather than a typical end-user ISP.
It's a constant cat-and-mouse game, where privacy enhancements lead to new identification strategies. To truly understand email performance, it's essential to monitor these trends and refine your metrics. Our guide on estimating real open rates with MPP can provide further insights.
Google Image Proxy and other mailbox providers
Beyond Apple MPP, Google also employs its own image proxy,
Google Image Proxy, to enhance user security and privacy. This service caches email images on Google's servers, preventing senders from tracking IP addresses or using malicious image content. While not identical to MPP, it creates a similar challenge for accurate open rate tracking. Understanding why emails show as opened with Google Image Proxy IP when the recipient hasn't opened them is a common troubleshooting issue.
Many other mailbox providers (MBPs), including Yahoo, also employ bots and caching mechanisms that pre-fetch images. This is often done for security scanning, to protect users from malicious content, or to optimize loading times. The presence of these bots means that proxy opens are not solely an Apple- or Google-specific issue, but a broader industry trend.
Adapting to evolving privacy measures
As the email landscape continues to evolve, ESPs and marketers must adapt to these privacy-first changes. Relying solely on open rates as a primary engagement metric is no longer sufficient. Instead, a more holistic view of engagement, focusing on clicks, conversions, and subscriber activity beyond the inbox, becomes paramount.
Traditional open metrics
IP-based geolocation: Used to determine subscriber location.
Accurate open rates: Direct measurement of unique opens.
Device detection: Identified the specific client used to open.
Modern engagement metrics
Click-through rates (CTR): Focus on actions taken after clicking.
Conversion metrics: Track purchases, sign-ups, or form submissions.
DMARC reports: Provide insights into email authentication and deliverability, unaffected by proxy opens. Using a tool like Suped's DMARC monitoring is invaluable for this.
Furthermore, ensuring strong email authentication via DMARC, SPF, and DKIM remains crucial for deliverability, as these mechanisms are unaffected by proxy opens. Tools like Suped offer comprehensive DMARC reporting and monitoring, which are essential for understanding your email ecosystem, regardless of how proxy opens are categorized.
The future of email engagement tracking
The shift towards enhanced email privacy, driven by initiatives like Apple MPP and Google Proxy Images, requires a continuous evolution in how we track and interpret email engagement. It's a challenging but necessary adaptation for all email professionals. By combining technical identification methods with a broader focus on engagement metrics, we can continue to optimize email programs effectively.
While pinpointing every single proxy open might remain elusive, the goal is to gather enough reliable data to make informed decisions. This includes refining internal tracking, adjusting reporting, and focusing on other strong indicators of subscriber interest, such as clicks and conversions. Remember that DMARC monitoring from Suped offers crucial deliverability insights, even in this new privacy-focused environment.
Views from the trenches
Best practices
Leverage IP addresses and ASN data to identify known proxy server ranges, particularly those published by Apple.
Analyze the timing of opens, flagging those occurring within seconds or minutes of delivery as potential proxy opens.
Shift focus from pure open rates to click-through rates and conversion metrics for more accurate engagement insights.
Ensure robust DMARC implementation and monitoring to maintain strong email authentication and deliverability.
Common pitfalls
Over-reliance on open rates as the sole measure of email campaign performance, leading to misinterpretation.
Assuming a generic user agent like 'Mozilla/5.0' always indicates a human open, ignoring proxy contexts.
Failing to account for image pre-fetching bots from various mailbox providers beyond just Apple and Google.
Not adjusting segmentation or automation workflows that are heavily dependent on immediate open signals.
Expert tips
Regularly review updated documentation from major mailbox providers (like Apple and Yahoo) regarding their proxy server IP ranges.
Implement a system to flag and potentially filter out proxy opens for cleaner engagement data, then analyze residual opens.
Focus on the long-term engagement of subscribers through other metrics that indicate true interest.
Educate marketing teams on the nuances of modern open tracking and the shift in reliable engagement indicators.
Expert view
Expert from Email Geeks says that for Apple Mail Privacy Protection (MPP), the main method for identification is by checking the IP addresses, as Apple documents all its exit points for these proxy requests.
2024-09-02 - Email Geeks
Expert view
Expert from Email Geeks points out that MPP used to have a very unique user agent string, but it is uncertain if that is still the case.
Apple Mail Privacy Protection (MPP), launched with iOS 15, iPadOS 15, and macOS Monterey, is designed to prevent email senders from learning a recipient's IP address and whether they have opened an email. It achieves this by routing all email image loads through a proxy server. When an email arrives in an Apple Mail inbox, even if the user hasn't explicitly opened it, Apple's servers pre-fetch all images, including tracking pixels. This means every email sent to an Apple Mail user with MPP enabled appears as an open.
Beyond Apple MPP, Google also employs its own image proxy, 
Many other mailbox providers (MBPs), including Yahoo, also employ bots and caching mechanisms that pre-fetch images. This is often done for security scanning, to protect users from malicious content, or to optimize loading times. The presence of these bots means that proxy opens are not solely an Apple- or Google-specific issue, but a broader industry trend.
