What does the ARC-Seal header indicate?
ARC (Authenticated Received Chain) headers preserve authentication results through message forwarding. ARC-Seal provides cryptographic seal validating the ARC chain, maintaining authentication across indirect routing.
Purpose: forwarding often breaks SPF and DKIM. ARC allows intermediate servers to vouch for original authentication, enabling receivers to trust forwarded messages that would otherwise fail.
Interpretation: ARC-Seal validates the chain is intact. Receivers trusting the intermediary can accept authentication despite forwarding. Useful for mailing lists and forwarding services.
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