5.7.29
Enhanced Status Code 5.7.29: ARC Validation Failed
Permanent failure
High severity
Security
RFC 8617
What it means
Enhanced Status Code 5.7.29 means “ARC Validation Failed.” The ARC (Authenticated Received Chain) validation failed for this message. ARC is used to preserve authentication results through email forwarding. A failed ARC chain indicates the message was improperly modified or the ARC signatures are invalid.
At a glance
Code5.7.29
Bounce typeHard (permanent)
SeverityHigh
CategorySecurity
What to doSuppress the address; do not retry
StandardRFC 8617
550 5.7.29 ARC validation failed: the Authenticated Received Chain on this forwarded message could not be verified.What does 5.7.29 mean?
Enhanced status code 5.7.29 indicates a failure in ARC (Authenticated Received Chain) validation. ARC is designed to preserve email authentication results as messages pass through intermediary servers like mailing lists and forwarding services. When ARC fails, it means the chain of authentication was broken.
This code is relevant when emails pass through forwarding services, mailing lists, or other intermediaries that modify messages. If the intermediary does not properly implement ARC, the receiving server may reject the message because it cannot verify the authentication chain.
How 5.7.29 plays out
Your server attempts delivery
The recipient server returns a permanent
5.7.29 rejectionThis is a hard bounce: the message will not be accepted as sent
Suppress the address and fix the root cause before resending
Where 5.7.29 sits: soft vs hard bounce
| Soft bounce (4xx) | Hard bounce (5xx) | |
|---|---|---|
| Nature | Temporary | Permanent |
| SMTP class | 4xx | 5xx |
| What to do | Let it retry | Suppress the address |
| Recoverable? | Often | No |
| 5.7.29 is | ✓ this code |
Common causes of 5.7.29
- ARC signatures in the message are invalid or malformed
- Intermediary server did not properly seal the ARC chain
- Message was modified after ARC sealing
- ARC implementation on the forwarding server is buggy or misconfigured
How to fix 5.7.29
- Ensure intermediary servers (mailing lists, forwarders) properly implement ARC
- Verify ARC sealing is configured on any servers that modify forwarded mail
- If you control the forwarding server, update ARC implementation to latest standards
- Consider implementing DKIM to provide authentication that survives forwarding
Frequently asked questions
What does error 5.7.29 "ARC validation failure" mean?
Error 5.7.29 means the receiving server could not validate the ARC (Authenticated Received Chain) headers on a forwarded or relayed email. ARC is a protocol that preserves email authentication results when messages pass through intermediary servers like mailing lists or forwarding services. When ARC validation fails, the chain of trust between the original sender and the final recipient is broken, and the server cannot verify the message's authenticity.
What causes ARC validation to fail?
ARC validation fails when an intermediary server does not properly seal the authentication chain, when the ARC headers are modified or corrupted in transit, or when the receiving server does not trust the ARC sealer. It also fails if the underlying SPF and DKIM authentication already failed before the intermediary processed the message. This is most common with email forwarding services, mailing lists, and security gateways that modify message content.
How do I fix a 5.7.29 ARC failure?
If you manage the intermediary server (forwarding service or mailing list), ensure it is configured to add valid ARC-Seal, ARC-Message-Signature, and ARC-Authentication-Results headers. If you are the original sender, ensure your SPF and DKIM are correctly configured so the initial authentication passes before the message reaches any intermediary. Contact your email provider or forwarding service to verify they support ARC sealing. Gmail, Microsoft 365, and major providers honor ARC seals from trusted sealers.
Is 5.7.29 related to DMARC failures?
Yes, 5.7.29 is closely related to DMARC. ARC was specifically designed to solve the problem of legitimate emails failing DMARC after being forwarded. When DMARC fails because forwarding broke SPF or DKIM, the receiving server checks for valid ARC results as a fallback. If ARC also fails (5.7.29), the message is rejected. Some servers may use the more general 5.7.26 ("multiple authentication checks failed") instead of the ARC-specific 5.7.29 code.
Related bounce codes
Sources & further reading
Reviewed by Jennifer Jackson, Email Deliverability Analyst · June 2026
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