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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