What could cause a DMARC RUF alert when DKIM/SPF are aligned and DMARC is set to p=none?

Key findings

• Subdomain vs. Organizational Domain DMARC: One common cause for RUF alerts, even with successful SPF and DKIM authentication, is if the DMARC record is published at the organizational domain but emails are sent from a subdomain that isn't explicitly covered or inheriting the policy as expected. While alignment might appear correct on the subdomain, the DMARC record on the organizational domain could be leading to issues.
• Reliability of RUF Reports: Forensic (RUF) reports are rare and often unreliable. Many ISPs either do not send them, or they may send false positives that do not accurately reflect a DMARC failure according to the policy. This unreliability makes troubleshooting based solely on RUF reports challenging.
• ISP-Specific Behavior: Certain Mailbox Providers (MBPs), like Yahoo, have specific ways of handling and reporting DMARC failures, which might not always align with general expectations. Some may send RUF reports only under special circumstances or through particular reporting platforms.
• The fo=1 Tag: The fo=1 tag requests forensic reports for any DMARC authentication failure, regardless of whether SPF or DKIM passed or failed. However, some ISPs may not strictly adhere to this, leading to reports that are not truly indicative of an issue if SPF/DKIM passed.

Key considerations

• Review DMARC Alignment for Subdomains: Ensure that the DMARC record's alignment policy (strict or relaxed) and its placement (organizational or subdomain level) correctly cover the sending subdomain. Issues can arise if the DMARC record is only on the organizational domain and a subdomain's DMARC doesn't align appropriately with it. Learn more about DMARC passing and identifier alignment.
• Focus on RUA Reports First: DMARC RUA (aggregate) reports provide a broader, more reliable overview of DMARC authentication results, showing volume and pass/fail rates. These are generally more useful for initial troubleshooting than RUF reports, which are forensic and often contain sensitive information. Understand DMARC tags and their meanings.
• Verify Original Email Headers: To accurately diagnose the issue, it's crucial to inspect the original email headers of the messages that triggered the RUF alerts. This provides the most precise information on how SPF, DKIM, and DMARC aligned at the time of delivery. A detailed guide on DMARC setup and configuration can be found here.
• Look for Spoofing or Phishing Attempts: If legitimate emails are passing DMARC, but RUF alerts are still being received, it might indicate actual spoofing or phishing attempts using your domain. RUF reports, while imperfect, are intended to alert you to such activity.

Key opinions

• Confusing RUF Alerts: Marketers often find RUF alerts perplexing, especially when DMARC headers indicate a pass for emails. The presence of these alerts, despite apparent success, suggests a discrepancy in how DMARC is being evaluated or reported.
• Subdomain vs. Main Domain: A common hypothesis among marketers is that the location of the DMARC record (e.g., on the organizational domain) can conflict with the DMARC pass status of a specific sending subdomain, leading to these alerts. This is a crucial aspect of why DMARC authentication might fail even with passing SPF/DKIM.
• Reliability of Forensic Reports: Many marketers express skepticism about the accuracy and prevalence of RUF reports, noting that few ISPs genuinely send them, and those that do might include false positives.
• Importance of Raw Headers: To properly troubleshoot, marketers emphasize the need to obtain the original email with full headers and DMARC RUA data, as the client's trimmed versions often lack critical diagnostic information.

Key considerations

• Investigate DMARC Record Placement: If sending from a subdomain, consider if a dedicated DMARC record for that subdomain is necessary, or how the organizational DMARC record's sp tag (subdomain policy) might be affecting interpretation. More on DMARC record and policy examples.
• Don't Over-Rely on RUF Reports: Marketers should primarily use DMARC aggregate reports (RUA) for monitoring and troubleshooting, as they are more consistently provided and offer a clearer picture of DMARC compliance across the email ecosystem. For initial setup, using p=none is recommended.
• Verify From Domain Alignment: Ensure the From header domain aligns with the SPF Return-Path (mailfrom) domain and the DKIM d= (signing) domain. Any mismatch can trigger DMARC alerts even if SPF or DKIM technically pass independently.

Key opinions

• Subdomain Policy is Key: Experts commonly point to the interplay between organizational domain DMARC records and subdomain sending practices as a primary suspect for unexpected RUF alerts. Ensuring correct DMARC setup for subdomains is critical.
• RUF Reports are Uncommon and Suspect: A consensus among experts is that RUF (forensic) reports are rarely sent by major ISPs, and when they are, their accuracy can be questionable. This makes any RUF alert, especially from sources like Yahoo (which generally doesn't send them), a point of scrutiny.
• ISP Discrepancies in fo Tag Handling: Some ISPs do not strictly honor the fo tag, which requests forensic reports for all failures. This can lead to misleading RUF reports even when DMARC authentication passes according to the sender's configured policies.
• Need for Complete Data: Without the full, untrimmed email headers and aggregate DMARC reports (RUA), diagnosing the precise reason for a RUF alert is extremely difficult. Experts stress the importance of comprehensive data.

Key considerations

• Verify DMARC Record for Subdomains: Confirm whether the DMARC record published on the organizational domain has a sp (subdomain policy) tag that correctly applies to the sending subdomain. Alternatively, ensure a dedicated DMARC record exists for the subdomain if required. This directly relates to why DMARC authentication might fail.
• Prioritize RUA Data: While RUF reports highlight specific email failures, aggregate reports (RUA) provide a statistical overview that is more reliable for identifying systemic issues or legitimate spoofing attempts. Use DMARC reports from Google and Yahoo as your primary diagnostic tool.
• Understand ISP-Specific Reporting: Be aware that not all ISPs send RUF reports, and those that do may have unique criteria or require specific partnerships for comprehensive data. The article on how DMARC works provides further context.
• Check for Spoofing: If all legitimate mail is passing DMARC and you're still receiving RUF alerts, this could genuinely indicate third-party spoofing or phishing attempts that are failing authentication, which is precisely what DMARC is designed to detect.

Key findings

• DMARC Policy p=none (Monitor): According to RFC 7489, p=none instructs receivers to take no specific action on emails that fail DMARC, but still generate reports. This is intended for initial deployment and monitoring.
• Forensic Reports (RUF): DMARC (RFC 7489) defines RUF as reports containing sanitized copies of messages that fail DMARC authentication. The fo tag dictates when these reports are sent.
• The fo=1 Tag: This flag specifies that forensic reports should be generated if any underlying authentication mechanism (SPF or DKIM) fails to produce an aligned pass. This means a RUF can be triggered even if SPF or DKIM technically pass but fail to align with the From domain as required by DMARC.
• Domain Alignment (SPF/DKIM): DMARC requires that either the SPF-authenticated domain or the DKIM-signed domain align (match or be a subdomain of) the From header domain. If SPF and DKIM pass their respective checks but fail this alignment, DMARC will still fail.

Key considerations

• Strict vs. Relaxed Alignment: DMARC allows for either relaxed (subdomain matches organizational domain) or strict (exact domain match) alignment for SPF and DKIM. Misunderstanding or misconfiguring this can lead to unexpected DMARC failures, even if SPF/DKIM technically pass. Zoho Mail's documentation on DMARC policy details this.
• Subdomain Policy (sp): The DMARC record's sp tag specifies the policy for subdomains. If this is not set or misconfigured, emails sent from subdomains might trigger alerts even if the main domain's DMARC is p=none. Understanding simple DMARC examples can help.
• Receiver Interpretation Variation: While DMARC is a standard, different mail servers may have subtle variations in their implementation or strictness when evaluating DMARC records and generating reports. This can lead to unexpected RUF alerts from certain providers like Yahoo.