Email open rate is not a reliable signal of program health, and for most inboxes it has not been one for years. Apple Mail, including Mail Privacy Protection, now accounts for 62.26 percent of tracked email opens, according to Litmus’s most recent client market share data.1 Litmus does not equivocate about what that means: opens routed through Mail Privacy Protection are not considered reliable opens. A metric contaminated at that scale is not a metric with some noise in it. It is a number that no longer measures what it claims to measure.
Mail Privacy Protection does not simply hide who opened a message. It removes the concept of opening from the signal entirely. Apple’s own documentation describes a two-relay proxy: the first relay sees a device’s IP address and nothing else, the second sees the remote content Mail downloaded and nothing else, and no single party holds both.2 The content, including a sender’s open-tracking pixel, downloads in the background as soon as a message arrives at the device, regardless of whether a person ever looks at it. The pixel fires, but nobody is there.
That is different than undercounting. Undercounting is a bias a program can correct for. A fabricated open event that fires on delivery rather than engagement is noise indistinguishable from signal at the individual message level. Segmentation built on open behavior, send-time optimization tuned to when subscribers historically opened, and A/B tests that pick a winning subject line by opens are all running on a number a server relay generated, not a subscriber.
The biggest objection is that click-through rate carries its own contamination. Corporate security gateways and some mail clients pre-fetch links to scan them for malware before a subscriber ever clicks, which inflates click counts the same way Mail Privacy Protection inflates opens. That objection is correct, and it does not rescue open rate. A metric with partial, variable noise a program can model against still beats one that fires on delivery for well over half a list by design. The question was never which metric is perfectly clean. It is which one still correlates with a human being on the other end.
Think about conversion instead. Where conversion is too sparse to be statistically useful, use click-to-open rate calculated against a denominator the program actually trusts rather than one Mail Privacy Protection has already corrupted. Deliverability signals that never depended on opens in the first place, bounce rate, complaint rate, and inbox placement, say more about list health than an open count ever did. None of this argues for dropping email open rate from a dashboard. It argues for stopping the practice of treating it as ground truth and starting to treat it as one noisy input among several, weighted accordingly.
Most marketing teams have not rebuilt their dashboards around that shift yet, which means most program health decisions being made this quarter are still keyed to a number Apple manufactures on a server before anyone reads the message.
Footnotes
- Litmus, Email Client Market Share: Trends & Statistics 2026, Litmus (Aug. 1, 2026), https://www.litmus.com/email-client-market-share. ↩︎
- Apple Inc., Mail Privacy Protection, Apple (last visited Sept. 19, 2026), https://www.apple.com/legal/privacy/data/en/mail-privacy-protection/. ↩︎
About the Author
Mickey Chandler is a Consultant & Attorney with over 28 years of experience in Email Deliverability & Privacy Law. He has a strong background in email authentication infrastructure (SPF, DKIM, DMARC), ISP and mailbox provider relations, anti-spam policy and compliance, CAN-SPAM and state anti-spam law gained through overseeing the Abuse & Compliance team at Salesforce Marketing Cloud, originating the ISP relations role at Informz (now part of Higher Logic), and working in the fight against spam since 1997. He holds a B.A. in Government, a B.S. in Computer Information Systems, and a J.D. from the University of Houston Law Center. He is a certified CIPP/US professional and a certified CIPM professional.
