Do proxy opens like Apple MPP confirm email inbox delivery and influence ISP perception?
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Jul 2025
Updated 18 Aug 2025
8 min read
The introduction of Apple Mail Privacy Protection (MPP) with iOS 15 fundamentally shifted how email opens are tracked. Historically, the humble open pixel was a key indicator for email marketers, signaling that a recipient had interacted with a message. With MPP, Apple's proxy servers began pre-fetching images, artificially inflating open rates and making it challenging to discern genuine engagement from machine activity.
This change raised immediate questions for the email community, particularly around the reliability of these proxy opens. Can we still rely on them as an indicator that our emails are landing in the inbox? More importantly, how do these machine-generated opens influence an Internet Service Provider's (ISP's) perception of our sending reputation and the overall deliverability of our emails? These are critical considerations for anyone focused on optimizing email performance.
The mechanics of Apple Mail Privacy Protection
When Apple introduced Mail Privacy Protection, the goal was to give users more control over their data, specifically by preventing senders from tracking their IP addresses and detecting when they opened an email. It works by routing all incoming mail through Apple's proxy servers. These servers then download all email content, including tracking pixels, before the user even sees the message.
This pre-fetching mechanism means that an open is registered regardless of whether the recipient actually opened the email themselves. For email marketers, this has skewed traditional open rate metrics, making them less reliable as a direct measure of human engagement. It's important to understand this fundamental shift when evaluating your campaign performance.
The impact extends beyond simple tracking numbers. Marketers previously used open data for segmentation, A/B testing, and understanding audience activity. Now, with a significant portion of opens being machine-generated, these insights are muddied. It requires a re-evaluation of how we define and measure email success, shifting focus to other, more reliable engagement indicators.
How MPP works
Proxy servers: Apple's private proxy network downloads email content, including images and tracking pixels.
Image pre-fetching: Images are downloaded at the time of email delivery, not when the user opens the email.
IP address masking: The user's IP address is hidden, preventing geolocation tracking.
Proxy opens and inbox delivery
The fundamental question is whether a proxy open confirms actual email inbox delivery. Generally, if an email triggers a proxy open (meaning its images were pre-fetched by Apple's servers), it's a strong indicator that the email was successfully delivered to the recipient's inbox. The logic here is that spam filters typically do not load images for emails they've quarantined or sent to the spam folder. If an email were flagged as spam, the proxy pre-fetching would usually not occur.
However, it's not a foolproof guarantee of human inbox placement, as there are always edge cases. Some advanced spam filters might interact with content in ways that could mimic a pre-fetch, but for the vast majority of cases, an Apple MPP-attributed open suggests the email made it past initial spam filtering and into a user's inbox or primary folder. This can be a useful signal to distinguish between emails that hit the inbox versus those that are blocked or land in spam.
While proxy opens can indicate delivery to the inbox, they don't necessarily confirm engagement. To learn more about how machine opens interact with spam folders, you can explore whether Apple MPP or Gmail machine opens occur on emails delivered to spam. It's a complex topic with nuances that warrant a deeper understanding of how prefetch and proxy opens are categorized.
Inbox delivery (pre-fetch)
High likelihood: If Apple's proxy servers pre-fetch images, the email likely landed in the inbox.
Passes initial filters: Pre-fetching typically occurs only after an email has passed preliminary spam checks.
Spam folder (no pre-fetch)
Images typically blocked: Spam filters usually prevent image loading for quarantined messages.
No proxy interaction: If an email is delivered to spam, Apple's servers typically won't pre-fetch.
ISP perception and true engagement
This is where a crucial distinction needs to be made. While proxy opens can signal inbox delivery, they do not directly influence an ISP's perception of your sender reputation. ISPs do not rely on your tracking pixels or open rates to determine whether your emails are valuable or spammy. Their systems have their own internal metrics for measuring engagement and sender trustworthiness.
ISPs analyze a multitude of factors to assess a sender's reputation and decide where to place their emails. These factors include, but are not limited to, complaint rates, bounce rates, spam trap hits, authentication records (SPF, DKIM, and DMARC), and, most importantly, positive user interactions. ISPs are interested in actual human engagement.
This means that while a proxy open might tell you something about delivery, it provides no direct signal to the ISP about how engaged the recipient is. An ISP is far more concerned with whether users are clicking on links, replying to messages, moving emails out of spam, or marking them as important.
For a deeper dive, this article on deliveries, opens, and clicks explains that image loads are visible only to senders and are a crude proxy for recipient interaction. It clarifies that while an image load likely means an email was delivered to the inbox, it doesn’t directly inform the ISP about user engagement. The ISP has its own sophisticated methods for assessing user interaction beyond what senders can track.
Signal
Sender's view (post-MPP)
ISP's view
Opens
High, but inflated due to proxy pre-fetching.
Not directly seen or relied upon as a primary signal.
Clicks
Reliable indicator of human engagement.
Strong positive signal.
Replies
High-intent human engagement.
Very strong positive signal.
Complaints
Negative feedback, indicates disinterest.
Strong negative signal, can lead to blacklisting.
Adapting to evolving deliverability metrics
Given that proxy opens do not provide direct insight into ISP perception, it's essential for email marketers to adapt their strategies. The focus must shift from relying on open rates to prioritizing actual human engagement. This involves a more holistic view of deliverability and sender reputation, leveraging other key metrics and best practices.
One primary area of focus should be click-through rates, conversions, and replies. These actions directly indicate that a recipient not only received but also found value in your email. ISPs closely monitor these positive interactions, as they signal that your mail is wanted and relevant to their users. Segmenting your audience based on click engagement rather than proxy opens can lead to better deliverability outcomes.
Maintaining a clean and engaged email list is paramount. Regularly remove inactive subscribers who show no signs of engagement over a prolonged period, as sending to unengaged recipients can negatively impact your sender reputation. Additionally, ensure your email authentication protocols like SPF, DKIM, and DMARC are correctly configured. These are fundamental to proving your legitimacy to ISPs and preventing your emails from being flagged as spam.
By focusing on metrics that truly reflect user engagement and maintaining strong sending practices, you can effectively navigate the evolving landscape of email privacy. This approach will lead to better inbox placement and a healthier sender reputation, ensuring your messages reach the intended audience and resonate effectively.
Views from the trenches
Best practices
Actively monitor engagement beyond open rates, focusing on clicks, replies, and conversions.
Segment your audience based on actual engagement metrics to prioritize sending to active recipients.
Regularly clean your email list by removing unengaged subscribers to improve overall list health.
Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly implemented and monitored.
Common pitfalls
Over-relying on proxy opens as a primary indicator of human engagement or inbox placement.
Failing to adapt segmentation strategies to account for inflated open rates from Apple MPP.
Neglecting other crucial deliverability signals that ISPs prioritize, such as complaint rates and spam trap hits.
Not maintaining a clean list, leading to lower engagement and potential blacklisting.
Expert tips
ISPs primarily focus on direct user actions like clicks, replies, and spam complaints, not external tracking pixels.
If an email triggers an Apple MPP proxy open, it's generally a good sign it landed in the inbox, as spam folders typically block image loads.
Proxy opens are useful for senders as a broad indicator of delivery, but don't inform the ISP's sender reputation assessment directly.
Focus on content relevance and list quality to drive true engagement, which is what ISPs value most.
Expert view
Expert from Email Geeks says that while there are edge cases, generally, if inboxes are proxying images and pre-fetching, those emails are making it into the inbox because spam placement does not typically load images.
2024-07-12 - Email Geeks
Expert view
Expert from Email Geeks notes that ISPs do not see image loads because they are a sender-only metric used as a crude proxy for recipient interaction.
2024-07-12 - Email Geeks
Key takeaways for email marketers
The advent of proxy opens through features like Apple Mail Privacy Protection has undeniably altered the landscape of email tracking. While these machine-generated opens can generally serve as a signal that your email has successfully bypassed initial spam filters and landed in the inbox, it's crucial to understand their limitations.
The most important takeaway is that proxy opens do not directly influence an ISP's perception of your sender reputation. ISPs utilize their own sophisticated, proprietary algorithms that prioritize genuine human engagement signals such as clicks, replies, and the absence of complaints. To maintain strong deliverability, marketers must shift their focus from vanity metrics to these authentic user interactions, coupled with robust email authentication and diligent list hygiene practices.
Apple Mail Privacy Protection (MPP) with iOS 15 fundamentally shifted how email opens are tracked. Historically, the humble open pixel was a key indicator for email marketers, signaling that a recipient had interacted with a message. With MPP, Apple's proxy servers began pre-fetching images, artificially inflating open rates and making it challenging to discern genuine engagement from machine activity.
