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Understanding Apple Mail Privacy Protection and Open Events


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With the release of Apple iOS 15, iPadOS 15, watchOS 8 and macOS 12 Monterey, Apple began offering a feature called Mail Privacy Protection(link takes you to an external page) (MPP). Mail Privacy Protection aims to block email senders from collecting recipients' data, including if and when recipients open a message.

This page will help you understand how MPP impacts email open statistics, how Twilio SendGrid indicates MPP-triggered opens, and how you can adjust your sending strategy with this email development in mind.

To understand how MPP affects open metrics, it's important to understand how conventional open statistics are collected.

Conventional open statistics

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Conventional open tracking across all email service providers is made possible by embedding an invisible image, often referred to as a pixel or tracking pixel, into each email. When a recipient opens the email, a request is sent to retrieve the images in the message, including the invisible pixel. The web request for the pixel indicates to the sender that the message has been opened. Open event data also returns the time of the request, user agent (browser or application from which the image request was made), and the approximate location with the requesting IP address.

Conventional Email Open Tracking Diagram.

Mail Privacy Protection and open statistics

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Apple's Mail Privacy Protection works by pre-fetching and caching messages, including the images in an email, whether the email has been opened by the intended recipient or not. This means any tracking pixels will be retrieved at the time Apple fetches the message's images, resulting in several downstream effects.

MPP Open Tracking Diagram.
  1. Senders cannot differentiate between a conventional open triggered by the intended recipient using Apple Mail and an open triggered by Apple's pre-fetch activity, which makes open statistics unreliable.
  2. Messages appear opened once even when the intended recipient has not opened the message, which artificially inflates unique open statistics.
  3. Apple also anonymizes the recipient's IP address and user agent, and then serves additional message opens to recipients from its own cache. This anonymizes the recipient's data, and repeat opens within Apple Mail are not returned to the sender.

Recipients on iOS 15 or macOS 12 Monterey can enable MPP using the Apple Mail client. Once enabled, Apple will begin pre-fetching and caching all mail sent to the recipient, regardless of where the recipient eventually accesses their mail.



See the Twilio SendGrid blog(link takes you to an external page) for more information on the MPP adoption we're seeing across SendGrid.

To understand how this happens, let's trace an example of the process for a message delivered to an MPP-enabled recipient.

  1. When an email is sent to the MPP-enable recipient, it will be delivered to the recipient's mailbox provider — let's assume the recipient uses Gmail.
  2. The recipient has configured their email in two ways: the Apple Mail App on their iPhone and the Gmail Web App on their laptop.
  3. After Gmail receives the email, the Apple Mail App will randomly pre-fetch the message and cache it, triggering an open.
  4. The recipient then opens the message using the Apple Mail App. The message will be retrieved from Apple's cache, and no data will be returned to the sender about this open.
  5. The recipient then also opens the message using the Gmail Web App. This activity outside Apple Mail will be served conventionally, delivering the pixel and returning the open data to the sender. In this example, this conventional open happens in addition to the MPP-triggered open from Apple.

How Twilio SendGrid is helping

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Twilio SendGrid identifies suspected MPP-triggered opens and relays this information to our senders using our Apple Open Indicator. When retrieving event data using the Twilio SendGrid Event Webhook, all open events will contain the Apple Open Indicator: sg_machine_open. This Boolean field is set to true when Twilio SendGrid believes the open has been triggered by Apple MPP activity.

Example open event

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email: '',
event: 'open',
ip: '',
sg_content_type: 'html',
sg_event_id: '<eventId>',
sg_machine_open: true,
sg_message_id: '<messageId>',
sg_template_id: '<dynamicTemplateId>',
sg_template_name: 'Hello, World!',
timestamp: 1635528511,
useragent: '<user agent value>'

Apple MPP opens triggered by conventional opens

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It's important to note that a conventional open may still be associated with an sg_machine_open: true event. Because all mail sent to a recipient who enables MPP will be handled the same way by Apple — whether it is pre-fetched and cached or triggered by a recipient opening the message — all mail to the recipient can generate an sg_machine_open: true.

A recipient might also open a message in the Apple Mail App before Apple fetches the images. This could be considered a conventional open because it happened before Apple's pre-fetching and caching. However, this otherwise conventional open will still return sg_machine_open: true. Twilio SendGrid respects MPP-enabled recipients requests for tracking privacy through Apple and, therefore, treats conventional opens for MPP-enabled recipients and MPP-triggered opens the same at this time.



The Apple Open Indicator is not meant to circumvent Mail Privacy Protection. Twilio SendGrid provides the Apple Open Indicator as a way for senders to rely on conventional engagement statistics while still honoring recipients' privacy preferences.

Apple and others will continue to adjust their approach to privacy. Twilio SendGrid actively monitors these changes throughout the industry and will continue to support our customers as the email landscape evolves. The Apple Open Indicator is just one of our approaches in assisting our senders.

What can you do as a sender

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Twilio SendGrid provides the Apple Open Indicator so that you can continue to rely on opens as a metric for all messages for which sg_machine_open is false. These opens will continue to function as a reliable engagement measure.

You may also look at other engagement indicators such as clicks. Because a click represents an intentional action by a recipient, a click is a strong measure of engagement. However, click engagement is typically far lower than open engagement, so you will need to calibrate accordingly.

The Twilio SendGrid blog also provides an in-depth discussion on approaches to engagement in a post-MPP world(link takes you to an external page).

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