The brief
Apple and WebKit have implemented various protections against web tracking, including blocking cross-site cookies six years ago, which was a significant step forward for privacy on the web. The tracking industry has since developed a new method called identity resolution, where third parties collect email addresses when users log in or sign up for newsletters, creating an opaque tracking ID linked to the email address.
Identity resolution involves third parties collecting email addresses and creating a tracking ID, which can be used to build a profile of a user's browsing habits or target ads across websites. This tracking ID is stored on the website and can be used for arbitrary purposes, even after a user logs out or unsubscribes from a newsletter, and can also be used for cross-device tracking.
To protect users against identity resolution, Safari and WebKit block network access to identity resolution infrastructure, preventing cross-site tracking by stopping the sending of email addresses to third-party servers. Additionally, iCloud+ subscribers can use the Hide My Email service, which generates unique, randomized email addresses to submit to websites, providing extra protection against email-based tracking.
