Do I need to implement ARC if I already have strict DMARC policies?

Yes, if your users frequently forward emails or participate in mailing lists. Strict DMARC policies (p=reject) will cause legitimate forwarded emails to be dropped because the forwarder breaks SPF alignment and often DKIM signatures. Implementing ARC allows receivers to evaluate the message's original authentication state, preserving deliverability for forwarded mail while maintaining strict DMARC enforcement.

What is the significance of the 'cv' (chain validation) tag in the ARC-Seal?

The 'cv' (chain validation) tag in the ARC-Seal indicates the outcome of the ARC validation performed by that specific intermediary. It can have values of 'none' (for the first instance, i=1), 'pass', or 'fail'. A final receiver uses the 'cv' value of the most recent ARC-Seal, combined with its own verification of that seal, to determine if the entire chain of custody is intact and trustworthy.

Free ARC Checker

Validate your Authenticated Received Chain (ARC) implementation to ensure email authentication results survive mailing lists and forwarders. Analyze ARC-Seal, ARC-Message-Signature, and ARC-Authentication-Results headers for RFC 8617 compliance.

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What Is Authenticated Received Chain (ARC)?

ARC (RFC 8617) is an email authentication protocol that bridges the gap DMARC leaves when messages transit through intermediaries like mailing lists. Forwarders break DKIM and SPF, causing DMARC failures. ARC has each intermediary cryptographically sign the original authentication results, creating a verifiable chain of custody for the final receiver to trust.

Why It Matters

Without ARC, legitimate forwarded email from mailing lists is dropped by strict p=reject DMARC policies. ARC preserves deliverability while maintaining strict DMARC enforcement for direct senders.

Common Mistakes

Broken ARC-Seal signatures from non-ARC-aware intermediaries, misconfigured DNS TXT records for ARC selectors, and out-of-sequence instance tags (i=) are the top causes of chain validation failures.

ARC_SEAL_i=1

SIGNATURE_VALID

AMS_i=2

cv=pass

ARC_VALIDATION_ENGINE

CHAIN_INTACT

How It Works

Input Domain

Type your domain into the ARC lookup tool above to begin validation.

Header Retrieval

Our engine retrieves and parses the ARC-Seal, ARC-Message-Signature, and AAR headers.

Chain Verification

We cryptographically verify every seal and signature in the chain, hop by hop.

Fix & Enforce

Follow our recommendations to repair broken chains and harden your forwarder setup.

Cryptographic Chain Validation

Performs rigorous cryptographic verification of the ARC-Seal (AS) and ARC-Message-Signature (AMS) headers. Validates RSA and Ed25519 signatures across the entire chain to ensure the integrity of the custodial path and detect tampering.

Header Syntax Inspection

Deep parsing of ARC-Authentication-Results (AAR), AMS, and AS headers for strict RFC 8617 syntax adherence. Checks for correct instance tags (i=), canonicalization algorithms (c=), and domain signatures (d=).

DMARC Survival Analysis

Evaluates how your ARC implementation interacts with strict DMARC policies (p=reject or p=quarantine). Identifies failure points in complex forwarding scenarios where traditional SPF and DKIM alignment breaks.

Multi-Hop Tracking

Visualizes and verifies each intermediary node in the ARC routing sequence, ensuring sequential integrity of instance tags (i=1, i=2, etc.) and verifying the cv (chain validation) status across all hops.

Key Rotation Diagnostics

Validates the DNS-published ARC public keys against the selectors (s=) used in the chain. Highlights outdated keys, weak key lengths below 2048-bit RSA, and ensures proper key rotation hygiene.

Algorithm Support Analysis

Confirms support for required cryptographic algorithms, verifying correct rsa-sha256 implementation and evaluating readiness for modern elliptic curve signatures like ed25519 for improved performance.

Frequently Asked Questions

How does ARC differ from DKIM and DMARC?

DKIM provides a cryptographic signature and DMARC enforces policy based on DKIM/SPF alignment, but both fail when intermediaries modify messages or change routing IPs. ARC (RFC 8617) supplements them by preserving original authentication results in a cryptographically verifiable chain, allowing downstream receivers to trust the initial authentication even after forwarding.

What causes an ARC chain validation to fail?

ARC chain validation fails when a non-ARC-aware intermediary modifies the message after an ARC seal has been applied, when DNS TXT records for ARC selectors are missing or misconfigured, or when instance tags (i=) are out of sequence. Any break in the cryptographic chain invalidates subsequent seals.

Do I need ARC if I already have strict DMARC policies?

Yes, especially if users forward email or participate in mailing lists. Strict p=reject DMARC drops legitimate forwarded emails because forwarders break SPF alignment and often DKIM signatures. ARC lets receivers evaluate the original authentication state, preserving deliverability while maintaining strict enforcement for direct senders.

What is the significance of the 'cv' tag in the ARC-Seal?

The 'cv' (chain validation) tag indicates the outcome of the ARC validation performed by a specific intermediary. It can be 'none' (for the first hop, i=1), 'pass', or 'fail'. The final receiver uses the 'cv' value of the most recent ARC-Seal, combined with its own seal verification, to determine if the entire chain is intact.

How does your tool verify the ARC-Authentication-Results (AAR) header?

Our tool parses the AAR header to extract SPF, DKIM, and DMARC results from previous hops. We verify RFC 8617 and RFC 7601 formatting compliance and cryptographically confirm the AAR has not been tampered with by validating the corresponding ARC-Message-Signature (AMS) that binds it to the message.

Can ARC prevent email spoofing on its own?

No. ARC is not designed to prevent spoofing and does not replace SPF, DKIM, or DMARC. It is a supplementary protocol that relies on initial authentication by SPF and DKIM. Its sole purpose is to securely convey those initial results across intermediaries that would otherwise break them.

Which cryptographic algorithms are supported for ARC signatures?

RFC 8617 mandates rsa-sha256 for broad compatibility. ed25519 is increasingly recommended for better performance and security with shorter keys. Our ARC checker validates both RSA (minimum 2048-bit) and Ed25519 signatures across the entire ARC chain.

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