Developing
Apple names no blocked companies, publishes no list and does not say whether hashed emails are covered.
In 60 seconds
- The WebKit post "Blocking Identity Resolution Infrastructure" says: "For the majority of users, their email address serves as a globally unique ID."
- Safari 27 blocks network access to third parties that turn email addresses into persistent IDs; the code change was 11 lines, merged February 13, 2026.
- The Trade Desk's September 21 bug report listed nine affected domains.
- It is unclear whether the block shipped in 27.0 or a later point release.
Impact Layer
- What changed
- Apple has now explained, in its own words, why Safari blocks identity-resolution domains.
- Why it matters
- Email-based identity underpins much of the open-web ad ecosystem, and Safari is a large share of that traffic.
- Who is affected
- Identity vendors, DSPs, publishers and advertisers with Safari audiences.
- Martech stack area
- Advertising, Data
- Stack impact
- Check which identity calls your site and ad stack make on Safari 27 and plan a fallback that does not depend on them.
- Business impact
- High Reported in PPC Land's October 20 edition from WebKit's post. Apple names no companies and does not say whether hashed emails are covered. The ID5 and OpenX 58% reach claim is the companies' own.
- Related technologies
- What to watch
- Whether Apple publishes a list, and the 27.2 release.
PPC Land’s October 20, 2026 newsletter reports a WebKit post, “Blocking Identity Resolution Infrastructure”, by John Wilander, Charlie Wolfe and Matthew Finkel.
What the post says
- Safari 27 blocks network access to third parties that turn email addresses into persistent IDs.
- “For the majority of users, their email address serves as a globally unique ID.”
- The code change was 11 lines, merged February 13, 2026.
- The Trade Desk’s bug report on September 21 listed nine affected domains. ID5 and OpenX have claimed a 58% Safari reach gain, a figure the companies supplied themselves.
Not stated
Apple names no blocked companies and publishes no list. It does not say whether hashed emails are covered, or whether the block shipped in version 27.0 or a later point release.
Our read
Apple’s stated reason is that an email address works as a universal ID. Any identity method built on it is exposed on Safari.
Sources
- PPC Land: Safari 27 blocks identity firms as search falls to 12% of publisher traffic (opens in a new tab)
Source for the WebKit post's statements and the open questions.