Apple introduces new tracking block in Safari

Apple announced on October 19 a new feature in Safari that blocks companies from tracking users based on their email address. This change was implemented without prior warning and has already started affecting the adtech industry’s revenue.

Blocking affects adtech revenue

Since the release of iOS 27 in mid-September, advertising requests no longer reach updated iPhones. Adtech companies have waited more than a month for Apple to officially explain the change, which targets a practice known as identity resolution.

How identity resolution works

As described by Apple in a WebKit blog post, identity resolution uses the email address a user enters during a login or newsletter subscription. A third party on the page captures this email and links it to an opaque identifier, which is then sent back to the website. This allows third parties to track user behavior and deliver targeted ads.

Apple clarifies tracking practices

Apple explains that these companies are not connection providers or newsletter services but are present solely to track users. With the latest iOS, iPadOS, macOS, and visionOS updates, Safari and WebKit now block connections to these third-party servers.

Apple filters by domain name

The company has chosen to filter access based on domain names, meaning changing the format of a request won’t bypass the restriction. Apple also states that personalization by the site itself is not considered tracking.

iCloud+ offers email protection

iCloud+ subscribers can use a feature called "Hide my email address," which generates a unique email address for each site. This helps protect the user’s real email while still allowing them to receive messages.

Apple’s blacklist remains secret

Apple has not specified which domains are on its blacklist or how companies can be removed. A WebKit ticket from an engineer at The Trade Desk lists nine blocked domains, including UID2 and ID5. One of these, adsrvr.org, was temporarily removed but is expected to remain blocked until the end of the month.

Adtech industry faces financial impact

For clients of Aditude, a monetization service, Safari on iPhones and iPads accounts for 12% of displayed ads and 11% of advertising revenue. On updated devices, the eCPM has dropped by more than 10%, though the overall impact is currently estimated at just 1% of revenue.

Apple continues anti-tracking campaign

Apple has been working against tracking for six years. Safari introduced Intelligent Tracking Prevention (ITP) in 2017 and blocked third-party cookies by default in 2020. The tracking industry has since developed "post-cookie" solutions, including identity resolution.

Criticism and Apple’s own advertising

Some in the adtech industry criticize Apple for potentially benefiting its own advertising efforts. The App Tracking Transparency feature, introduced in 2021, requires apps to ask for permission before tracking users. Meta estimated a $10 billion revenue loss in 2022 due to these changes.