When you're diving into email authentication, especially with DMARC, you might encounter an ARC (Authenticated Received Chain) verdict that includes 'cv=fail'. This specific result indicates that the ARC chain validation has failed. It's a critical signal because it tells the receiving mail server that something went wrong during the re-authentication process of an email that has been forwarded or passed through an intermediary.
The purpose of ARC is to preserve email authentication results (SPF, DKIM, and DMARC) through multiple hops, like forwarding services or mailing lists. These intermediaries often modify emails, which can break standard authentication. ARC acts as a chain of trusted authenticators, allowing the final receiver to verify the email's original authentication status, even if subsequent modifications would normally cause DMARC to fail. The 'cv' tag within the ARC-Seal header is specifically designed to indicate the chain validation status.
Understanding this result is crucial for maintaining good email deliverability. A 'cv=fail' means the receiving server couldn't verify the integrity of the ARC chain, which could lead to DMARC failures and potentially push your emails into the spam folder. Let's explore what triggers this failure and how to address it.
Understanding ARC Chain Validation Status
What 'cv=fail' means
The 'cv' tag in an ARC-Seal header stands for Chain Validation. When it presents a 'fail' result, it signifies that the cryptographic signatures within the ARC chain itself could not be verified. Each ARC-Seal in the chain is signed by an intermediary, and these signatures attest to the message headers and original authentication results at that point in the journey. If any of these seals are broken or cannot be validated, the chain integrity is compromised, leading to 'cv=fail'.
Think of it like a notarized document passing through several hands. Each person adds their own seal, confirming what was in the document when they received it. If a later recipient finds a broken or fraudulent seal, they can't trust the chain of custody for the document. Similarly, in ARC, if an intermediary fails to properly sign the message, or if a message modification occurs that invalidates a previous signature, the entire chain becomes untrustworthy. You can find more details in the RFC 8617 specification for ARC.
This contrasts with a cv=pass result, which means the ARC signatures were cryptographically valid, confirming the integrity of the authentication chain. The 'cv=fail' does not necessarily mean the email is spam, but it does mean that the DMARC policy decision for that email could be more stringent because the ARC mechanism intended to help it pass wasn't valid. It's a key indicator for mail receivers to be more cautious about the email's true origin.
Why 'cv=fail' occurs and its impact
Common causes for ARC chain validation failure
Several factors can lead to a 'cv=fail' result, primarily related to how intermediaries handle or modify an email. One common cause is improper implementation of ARC by a forwarding server or mailing list. If an intermediary doesn't correctly apply an ARC-Seal header, or if the cryptographic signature within it is invalid, the chain breaks.
Another significant factor is email modification after an ARC-Seal has been applied. Email forwarding services, anti-spam filters, and mailing list managers might alter message headers or body content. If these changes occur without the intermediary correctly resealing the ARC chain, previous signatures become invalid. For example, some services might append footers or modify the subject line, which can inadvertently cause a validation failure. This is why ARC re-authenticates an email at each hop to maintain integrity.
Broken chain scenarios
Misconfigured intermediary: Forwarding servers that don't correctly sign their ARC-Seal or use an invalid private key will cause the 'cv=fail' result.
Header alterations: Adding or removing headers (like Authentication-Results) by a server that doesn't re-seal the ARC can break the cryptographic integrity.
Body modifications: Changes to the email body, even small ones like tracking pixels or disclaimers, can invalidate DKIM signatures and subsequently the ARC chain.
Impact on DMARC
DMARC failure: Without a valid ARC chain, DMARC will fall back to assessing the message based on its current SPF and DKIM status, which are likely to fail due to forwarding.
Reduced deliverability: Emails with 'cv=fail' are more likely to be marked as spam or rejected, affecting your reputation and inbox placement (blocklist status).
Spoofing concerns: Receiving servers might interpret a broken ARC chain as a potential attempt at email spoofing or malicious activity.
Ultimately, a 'cv=fail' means the recipient mail server cannot trust the chain of authentication results presented by ARC. This forces them to rely solely on the current, often failing, SPF and DKIM checks, which can lead to email rejections or misclassification as spam. It's a clear signal that the ARC protocol's intent to preserve authentication through forwarding has been undermined.
Diagnosing and troubleshooting 'cv=fail'
Diagnosing and troubleshooting 'cv=fail'
To diagnose a 'cv=fail' issue, you'll need to examine the email headers for messages that are experiencing this problem. Look for the ARC-Authentication-Results header and specifically the 'cv=' tag. You'll often see other related tags like 'arc=fail' in the arc-status field, confirming a failure in the overall ARC processing. Identifying the specific hop where the chain broke can be challenging without access to intermediary server logs.
Example of ARC 'cv=fail' in email headerstext
ARC-Authentication-Results: i=1; mx.google.com; arc=fail
dkim=fail header.i=@example.com header.s=s1024;
spf=fail (google.com: domain of sender@original.com does not designate
192.0.2.1 as permitted sender) smtp.mailfrom=sender@original.com;
dmarc=fail (p=none sp=none) header.from=original.com
ARC-Message-Signature: i=1; a=rsa-sha256; cv=fail; d=mail.intermediary.com; s=arcselector;
h=From:To:Subject:Date:Message-ID:MIME-Version:Content-Type;
bh=SomeBase64Hash;
b=SomeOtherBase64Hash
Monitoring your DMARC reports is the most effective way to identify if 'cv=fail' results are affecting your email deliverability. These reports provide aggregated data on how your emails are performing, including authentication results and ARC verdicts. A high number of DMARC failures attributed to 'cv=fail' through an ARC-aware intermediary would signal a problem.
If you are using a forwarding service or mailing list, ensure they have proper ARC implementation. If you control the intermediary, verify your ARC signing configuration. For end-users receiving these emails, a 'cv=fail' typically isn't something they can directly fix. It points to an issue upstream with the sender's or intermediary's configuration, which can lead to emails landing in the spam folder or being rejected by strict DMARC policies at the final destination.
Mitigating the impact of 'cv=fail'
Mitigating the impact of 'cv=fail'
To mitigate the negative impact of 'cv=fail', the primary focus should be on ensuring that any intermediary servers or services that handle your emails correctly implement and manage ARC. This means checking that they are properly generating ARC-Seal headers and updating the ARC-Authentication-Results header at each hop. If you're using a third-party forwarding service, inquire about their ARC support and best practices.
For email senders, particularly those sending through complex pathways that might involve forwarding, understanding how to implement ARC is key. While you can't control every intermediary, ensuring your initial email setup is robust (with strong SPF and DKIM) gives ARC the best foundation to work with. If ARC is being properly adopted, it helps in maintaining your sending reputation across the entire email ecosystem, helping to keep you off any email blacklist or blocklist.
Key strategies to prevent 'cv=fail'
Choose ARC-aware services: Select email service providers or forwarding solutions that explicitly support ARC and commit to maintaining its integrity.
Minimize message modifications: Reduce unnecessary changes to email headers or body content by intermediaries when possible.
Regular DMARC monitoring: Actively review your DMARC reports for ARC-related failures. Tools like Suped offer detailed insights and AI-powered recommendations to help you fix these issues.
Educate partners: If you collaborate with other organizations that forward your emails, ensure they understand the importance of ARC validation.
Ultimately, a 'cv=fail' is a signal that the protective measures of ARC are not functioning as intended, potentially exposing your emails to DMARC failure. Proactive monitoring and collaboration with your email ecosystem partners are essential for maintaining strong email authentication and deliverability.
Conclusion
Enhancing DMARC visibility and control
While ARC helps with forwarding, the ultimate goal is to ensure robust email authentication for your domain. Implementing and maintaining DMARC is paramount. By leveraging DMARC monitoring and reporting, you gain clear visibility into how your emails are being authenticated and where failures like 'cv=fail' are occurring. This allows you to identify specific problems, whether they stem from your sending infrastructure or from external intermediaries.
Suped offers comprehensive DMARC monitoring solutions that simplify the complex world of email authentication. Our platform aggregates DMARC reports and provides actionable insights, helping you understand not just that a 'cv=fail' occurred, but also what steps to take to resolve it. Our AI-powered recommendations can guide you through the process of strengthening your DMARC policy and improving deliverability. We also provide a generous free plan, making DMARC accessible to businesses of all sizes.
By actively monitoring your authentication results and leveraging tools designed for DMARC, you can ensure your domain is protected from spoofing and that your legitimate emails reliably reach their intended recipients. A 'cv=fail' result is just one piece of the puzzle, and with the right tools, you can transform it from a cryptic error into an actionable insight for better email security.
Remember, email authentication is an ongoing process. Regular review of your DMARC reports, including ARC results, is essential to adapt to changes in your email sending practices and to maintain optimal deliverability. Using a platform like Suped empowers you with the knowledge and tools to stay on top of your email security posture.
