When discussing email security, the term ARC often comes up, but its specific version can sometimes be a point of confusion. Many search results might point to other technologies that use "ARC" in their names, such as web browsers or gaming updates. However, in the context of email authentication, ARC refers to the Authenticated Received Chain.
The Authenticated Received Chain (ARC) is an email authentication protocol designed to allow legitimate email forwarders to preserve email authentication results. This is crucial because standard authentication methods like SPF and DKIM can break when an email is forwarded, potentially leading to legitimate messages being marked as spam or rejected. Understanding the current version helps us leverage its full capabilities for improved deliverability and security.
The official ARC protocol standard
The official ARC protocol standard
The current and widely adopted version of the ARC protocol is defined by RFC 8617, published in July 2019. This document outlines the technical specifications for how ARC works, including the structure of its header fields and the cryptographic processes involved in maintaining the chain of authentication.
There isn't a subsequent, officially standardized version (like ARCv2) in widespread use for email authentication purposes. When you see references to ARC in email security discussions, it almost invariably refers to this initial, foundational protocol. The protocol's design aims for flexibility, allowing it to adapt without requiring a new version number for minor enhancements or clarifications.
The stability of ARC version 1 means that email administrators and DMARC monitoring services can rely on a consistent standard when implementing and interpreting ARC results. This consistency is vital for maintaining interoperability across various email providers and ensuring the integrity of forwarded messages.
Key ARC header fields
Key ARC header fields
ARC introduces three primary header fields that work together to establish and verify the authentication chain. These headers are added to an email by an intermediate mail server when it processes a message. Each header plays a specific role in preserving the original authentication results.
Header Field
Purpose
ARC-Authentication-Results
This header carries the authentication results (like SPF and DKIM) received by the current hop. It helps form the chain of authentication results, which can be seen as the ARC chain concept.
ARC-Message-Signature
This header contains a cryptographically signed copy of key message headers and content. It's essentially a signature of the message's state at that point in its journey.
ARC-Seal
This header acts as a cryptographic seal, binding together the ARC-Authentication-Results and ARC-Message-Signature headers from the current and previous hops. It ensures the integrity of the authentication chain.
By understanding these components, we can better appreciate how ARC maintains trust in forwarded emails. The three main ARC header fields collectively assure recipients that the email's authentication status has been transparently preserved.
Why ARC matters for deliverability
Why ARC matters for deliverability
ARC is particularly valuable in scenarios where email forwarding is common, such as mailing lists or personal email redirection. Without ARC, a legitimate email that passes SPF and DKIM at the original sender might fail these checks after being forwarded, because the forwarding server changes aspects of the email that invalidate the original authentication.
Email forwarding without ARC
SPF breaks: The forwarding server's IP address often doesn't match the original sender's SPF record, leading to SPF failure.
DKIM issues: Changes to the message body or headers by the forwarding server can invalidate the original DKIM signature.
DMARC failure: Without SPF or DKIM alignment, the email fails DMARC, potentially leading to quarantine or rejection.
Email forwarding with ARC
Authentication preserved: The ARC chain provides a verifiable history of authentication results.
Trust for forwarders: Receiving servers can trust that legitimate forwarding has occurred without malicious alteration.
Improved deliverability: Legitimate forwarded emails are more likely to reach the inbox, reducing false positives.
ARC ensures that the authentication results from the initial sending server are cryptographically signed and passed along the forwarding chain. This allows the final receiving mail server to validate the entire chain, even if SPF or DKIM fail at intermediate hops. This capability is vital for organizations that rely on mailing lists, helpdesk systems, or other forwarding mechanisms, as it directly impacts email deliverability and reputation.
Monitoring and implementing ARC for better email security
Monitoring and implementing ARC for better email security
For email senders, understanding ARC's role in DMARC authentication is paramount. While you typically don't directly implement ARC headers (forwarding servers do this), you benefit from its presence in the email ecosystem. Monitoring your DMARC reports, which contain ARC results, is essential for gaining a complete picture of your email flow and identifying potential deliverability issues.
Enhance DMARC monitoring with Suped
Suped provides advanced DMARC reporting and monitoring, including detailed insights into ARC validation outcomes. Our platform offers AI-powered recommendations to help you interpret complex authentication data and take actionable steps to fix issues. With our unified platform, you can oversee DMARC, SPF, and DKIM alongside blocklist and deliverability insights, ensuring comprehensive email security.
Real-time alerts: Stay informed about any authentication failures or policy changes.
SPF flattening: Avoid SPF lookup limits with our intelligent optimization.
MSP and multi-tenancy dashboard: Manage multiple client domains efficiently from a single interface.
Properly configured DMARC, SPF, and DKIM are the foundation of good email deliverability. By keeping an eye on your DMARC reports, you can ensure that legitimate emails are reaching their intended inboxes, protecting your domain's reputation and ensuring compliance with modern email security standards.
Even with ARC in place, misconfigurations in your DMARC, SPF, and DKIM records can still lead to deliverability problems. Regularly reviewing your authentication setup is a best practice for all email senders.
Conclusion
Conclusion
While email authentication can seem complex with various protocols, the Authenticated Received Chain (ARC) plays a critical role in maintaining email trust. The current ARC header version in use is version 1, as defined by RFC 8617. This standard provides a robust mechanism for preserving authentication results across forwarding hops, which is essential for ensuring your legitimate emails reach their destination.
By understanding ARC and actively monitoring your DMARC reports, you empower your email program to overcome common deliverability challenges. This commitment to email authentication strengthens your domain's reputation and guards against spoofing and phishing attacks.
