How does ARC impact email deliverability for DMARC-enforced domains, and what are the best practices for marketers?

However, the effectiveness of ARC heavily relies on widespread deployment and established trust relationships among Mail Transfer Agents (MTAs). Without these, ARC offers only partial mitigation for authentication breakage, primarily benefiting scenarios like discussion mailing lists and some vanity domain forwarding. For marketers, ARC is not a standalone solution or a magic bullet to bypass DMARC enforcement challenges. Instead, robust DMARC implementation and consistent email sending best practices remain paramount for ensuring email deliverability.

Key findings

• ARC's purpose: ARC is designed to allow DMARC-protected messages to remain authenticated even after being modified or forwarded by intermediaries, preventing DMARC failures that would otherwise occur. It provides a chain of authentication results.
• Deployment challenge: For ARC to function effectively, it must be deployed on every Mail Transfer Agent (MTA) in the forwarding chain. This widespread adoption is currently not sufficient.
• Trust relationships: Out-of-protocol trust relationships must be established between MTA operators for ARC signatures to be respected as valid, a condition not yet fully formed across the email ecosystem.
• Limited scope: ARC primarily offers partial mitigation for authentication breakage in specific scenarios like discussion mailing lists and some vanity domain forwarding, rather than a universal fix for all DMARC failures due to modification.
• DMARC's impact: If a DMARC policy (especially p=quarantine or p=reject) is enforced on a domain, and the email's authentication breaks en route without ARC's intervention, the mail will likely not be delivered, as noted by experts.

Key considerations

• Marketer reliance: Marketers should not solely rely on ARC to ensure deliverability for DMARC-enforced domains, as its current effectiveness is conditional on factors outside their control.
• DMARC best practices: The primary focus for marketers remains adhering to robust DMARC best practices to minimize authentication failures regardless of ARC's presence.
• Consistent authentication: Ensure all emails are authenticated correctly with both SPF and DKIM, and that messages are composed in a way that is resilient to content rewriting.
• Proactive monitoring: Ongoing monitoring of DMARC reports is essential to identify and address any authentication failures or deliverability impacts, especially with new sender requirements from providers like Outlook and Gmail.

Key opinions

• Limited marketer impact: Many marketers do not see ARC as a significant factor they can directly leverage to improve deliverability, especially unless they are an ISP or a large mail forwarder.
• Not a DMARC fix-all: ARC is generally not considered a solution that will save marketers from poor DMARC implementation or authentication issues arising from their own sending practices.
• DMARC's inherent nature: DMARC, particularly with stronger policies, is designed to reduce deliverability of unauthenticated mail. ARC is a nuanced attempt to mitigate specific scenarios of authentication breakage, not to circumvent DMARC's core function.
• Direct impact on spam: Even if ARC becomes widely adopted, its effect on reducing DMARC failures for legitimate emails might be minimal compared to the impact of senders being diligent about their own email authentication and content.

Key considerations

• Foundational DMARC practices: Marketers must prioritize robust DMARC implementation, including proper SPF and DKIM setup and alignment, as this is the most impactful factor within their control for deliverability.
• Content robustness: Send emails that are not only syntactically correct but also resilient against semantic-less content rewriting (modifications that don't change meaning but can break authentication).
• Monitoring and reporting: Regularly review DMARC reports to detect where and why authentication might be failing, enabling prompt adjustments to sending practices or DMARC policies.
• Gradual DMARC enforcement: Adopt a gradual approach when implementing stricter DMARC policies (e.g., moving from p=none to p=quarantine or p=reject) to monitor impact and troubleshoot issues before full enforcement. Consider how Gmail and Yahoo requirements for 2024 impact this.

Key opinions

• Theoretical benefit: ARC is theoretically designed to allow DMARC-protected messages to remain valid even when modified in transit, a common issue with mail forwarding.
• Deployment limitations: Its effectiveness is hindered because ARC is not widely deployed on every MTA in the forwarding chain, nor are the necessary trust relationships sufficiently formed among operators.
• Niche use cases: ARC's primary benefit is seen in addressing authentication breakage for discussion mailing lists, with a secondary, minor benefit for vanity domain forwarding.
• No magic solution: Experts strongly caution that ARC is not a magic bullet to fix DMARC failures for marketers, nor does it excuse poor sending practices.
• Sender responsibility: Deliverability ultimately relies on senders being exquisitely careful about how they send mail, ensuring proper authentication and message composition.

Key considerations

• Beyond ARC: Marketers must focus on comprehensive DMARC best practices, including authoritarian mailstream management across their enterprise, to reduce authentication breakage.
• Robust message composition: Emails should be structured to be robust against semantic-less content rewriting, which can inadvertently break authentication.
• Continuous monitoring: It is crucial to monitor DMARC reports regularly to ensure that email authentication is consistent and that the impact of DMARC on deliverability remains minimal.
• Proactive troubleshooting: Be prepared to troubleshoot DMARC failures by examining email headers for ARC-Seal and other authentication results.
• Understanding DMARC purpose: Recognize that DMARC, particularly with an enforcement policy (other than p=none), is designed to potentially lower deliverability of unauthenticated mail for security reasons.

Key findings

• Authentication preservation: ARC provides a mechanism to convey and validate email authentication results (SPF, DKIM, DMARC) across hops in the email delivery path, especially when messages are modified by intermediaries.
• Chain of custody: It establishes an authenticated chain of custody by adding a new set of headers (ARC-Authentication-Results, ARC-Message-Signature, and ARC-Seal) with cryptographic signatures at each hop.
• Intended scenarios: ARC is specifically designed to address situations where legitimate mail forwarding (like mailing lists or forward-to-account services) can break traditional SPF and DKIM authentication.
• DMARC compatibility: It enables DMARC-enforced domains to receive forwarded email without it failing DMARC due to intermediate changes, provided the ARC chain is valid and trusted by the recipient.

Key considerations

• Trust and validation: For ARC to be effective, receiving mail servers must validate the ARC chain and trust the ARC-signing intermediaries. This trust is built over time and through reputation.
• Limited scope for senders: From a sending domain's perspective, while DMARC enforcement is within their control, ARC implementation relies on the receiving and intermediary mail servers.
• Supplemental, not replacement: ARC supplements, but does not replace, the need for robust SPF and DKIM authentication at the initial sending stage.
• Role in DMARC reporting: DMARC reports provide insights into authentication failures, including those related to forwarding. Understanding DMARC policy examples and ARC's role can help interpret these reports more accurately.