ARC-Authentication-Results
The ARC header in which an intermediary records the SPF, DKIM, DMARC and ARC results it saw on arrival, numbered with the ARC instance.
What it means
The ARC-Authentication-Results (AAR) header copies the format of Authentication-Results, adding an i= instance number. Each ARC set has exactly one, combining all results the handler obtained, however many Authentication-Results headers it wrote.
Its value lies in history: the AAR at i=1 shows what the first ARC-aware handler saw before any forwarding changed the message, for example dkim=pass and dmarc=pass for the original sender. A final receiver that trusts that handler can use it to accept the forwarded copy.
Example
ARC-Authentication-Results: i=1; mx.lists.example.org; dkim=pass header.d=example.com; spf=pass smtp.mailfrom=example.com; dmarc=pass header.from=example.comRelated terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 8617: The Authenticated Received Chain (ARC) Protocol, section 4.1.1rfc-editor.org
- Google Workspace Admin Help: ARC email authenticationknowledge.workspace.google.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes