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Module 11 · Lesson 32 of 37

ARC: Authenticated Received Chain

Part of The Complete Email Deliverability Course — Advanced Protocols.

ARC solves authentication breaking during email forwarding.

When forwarding services modify messages:

  • SPF fails (new sending IP)
  • DKIM may fail (body modifications)
  • Legitimate mail fails DMARC

ARC adds three headers at each hop:

  1. ARC-Authentication-Results — Snapshot of SPF/DKIM/DMARC at this hop
  2. ARC-Message-Signature — DKIM-like signature over the message
  3. ARC-Seal — Signature over all previous ARC headers

The final receiver validates the ARC chain and can use the first hop's results to override a DMARC failure.

Supported by: Gmail, Microsoft 365, Yahoo, Proton Mail

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