How can I troubleshoot DMARC failures and identify the cause of authentication issues?

Summary

Troubleshooting DMARC failures requires a multifaceted approach involving technical configuration, proactive monitoring, and policy implementation. It begins with meticulously inventorying all email sending sources (ESPs, third-party services) and their authentication settings (SPF, DKIM). Implementing a DMARC vendor streamlines this process by providing reports, dashboards, and automated alerts to identify unauthorized senders, misconfigurations, or potential spoofing attempts. Understanding and addressing the underlying causes of SPF and DKIM failures, such as SPF PermErrors, insufficient DKIM key sizes, or DKIM verification issues, is critical. Correct DMARC record syntax, SPF flattening to prevent lookup limits, and proper reverse DNS (PTR) record configuration also contribute to successful DMARC implementation. Finally, initiating a 'p=none' DMARC policy allows monitoring and issue resolution before enforcing stricter policies that could inadvertently block legitimate email. DMARC alignment, requiring both SPF and DKIM to pass and align with the domain, is a key aspect of the process.

Key findings

  • Comprehensive Inventory: Maintaining a complete list of all email sending sources with their authentication settings is fundamental.
  • DMARC Vendor Benefits: Utilizing a DMARC vendor simplifies troubleshooting through comprehensive reporting and automated alerts.
  • SPF/DKIM Troubleshooting: Addressing the root causes of SPF and DKIM failures is crucial for DMARC compliance.
  • Technical Configuration: Correct DMARC record syntax, SPF flattening, and proper PTR records are essential for authentication success.
  • Monitoring Before Enforcement: Starting with a 'p=none' DMARC policy allows for problem identification without disrupting email delivery.
  • DMARC Alignment Importance: Strict DMARC alignment, where both SPF and DKIM pass and align with the domain, is required.

Key considerations

  • Data Visibility: Without a comprehensive inventory and effective reporting, identifying DMARC failure sources becomes difficult.
  • Technical Expertise: Understanding and addressing technical configuration issues requires specialized knowledge.
  • Gradual Implementation: Enforcing stricter DMARC policies prematurely can lead to the unintended blocking of legitimate email.
  • Ongoing Maintenance: DMARC compliance requires continuous monitoring, maintenance, and adaptation as email infrastructure evolves.
  • Third-Party Integration: Ensuring all third-party senders used on behalf of your domain are properly configured is vital.

What email marketers say
9Marketer opinions

Troubleshooting DMARC failures involves a multi-faceted approach. Key actions include meticulously cataloging all email sending sources (ESPs, third-party services, etc.) with their authentication configurations, and continuously monitoring DMARC reports for anomalies and trends. Technical aspects include ensuring SPF records are properly flattened and free of errors (PermError), DKIM key sizes meet recommended standards (1024+ bits), and reverse DNS (PTR) records align with sending domains. Implementation strategies involve starting with a 'p=none' DMARC policy to monitor and adjust configurations before enforcing stricter policies. Proper authentication for all sending sources, including third parties, is crucial.

Key opinions

  • Source Inventory: Maintain a comprehensive list of all email sending sources and their authentication settings.
  • Report Monitoring: Continuously monitor DMARC reports to identify anomalies and unauthorized sending sources.
  • SPF Optimization: Implement SPF flattening and correct any SPF record errors to prevent authentication failures.
  • DKIM Key Size: Use a DKIM key size of at least 1024 bits, with 2048 bits recommended, for adequate security.
  • Reverse DNS Alignment: Ensure reverse DNS (PTR) records match the sending domain to improve sender reputation.
  • DMARC Policy Implementation: Start with a 'p=none' DMARC policy for monitoring before enforcing stricter policies.
  • Third-Party Authentication: Ensure proper SPF and DKIM configuration for all third-party senders.

Key considerations

  • Comprehensive Tracking: Without a comprehensive list of sending sources and authentication configurations, identifying the cause of DMARC failures becomes significantly more difficult.
  • Proactive Monitoring: Regularly analyzing DMARC reports is crucial for early detection of unauthorized sending and misconfigurations.
  • Technical Accuracy: Errors in SPF records, insufficient DKIM key sizes, and incorrect reverse DNS can all lead to DMARC failures.
  • Gradual Enforcement: Enforcing stricter DMARC policies too early can inadvertently block legitimate email; a gradual approach is recommended.
  • Third-Party Oversight: Failure to properly authenticate third-party senders can compromise overall DMARC compliance.
Marketer view

Email marketer from GlockApps shares that using an insufficient DKIM key size can lead to authentication issues. Ensure your DKIM key is at least 1024 bits, with 2048 bits being the recommended standard, to provide adequate security and prevent DKIM failures.

July 2021 - GlockApps
Marketer view

Email marketer from URIports explains that an SPF PermError can cause SPF checks to fail. This error occurs when the SPF record has syntax errors, includes too many lookups, or is otherwise invalid. Correcting the SPF record is essential for proper email authentication.

February 2023 - URIports
Marketer view

Email marketer from LinkedIn explains that ensuring proper authentication for third-party senders is critical for DMARC compliance. If you use ESPs or other services to send email on your behalf, ensure they are properly configured with SPF and DKIM, and that these are aligned with your domain.

March 2021 - LinkedIn
Marketer view

Email marketer from Stack Overflow explains that the DMARC policy (p=none, p=quarantine, p=reject) determines how email receivers handle emails that fail DMARC checks. Implementing a 'p=none' policy initially allows you to monitor failures without impacting deliverability, while stricter policies ('quarantine' or 'reject') offer greater protection against spoofing once you've resolved the issues.

November 2022 - Stack Overflow
Marketer view

Email marketer from Mailjet explains that continuous monitoring of DMARC reports is essential for identifying trends and anomalies. Regular analysis helps detect unauthorized sending sources, misconfigurations, or potential spoofing attempts, allowing for proactive intervention.

August 2023 - Mailjet
Marketer view

Email marketer from Email Geeks suggests maintaining a list of all email sending vectors, including ESPs, with details on key settings, DNS records, authentication status, usage, and reputation risk to better organize and identify potential authentication issues.

December 2024 - Email Geeks
Marketer view

Email marketer from EmailGeekForum explains that reverse DNS (PTR record) should match your sending domain. Discrepancies in the PTR record can negatively affect your sender reputation and lead to DMARC failures.

June 2022 - EmailGeekForum
Marketer view

Email marketer from EasyDMARC shares that SPF flattening is a technique to prevent SPF lookup limits. If your SPF record exceeds the maximum number of DNS lookups, SPF authentication can fail. Flattening helps optimize the record to stay within these limits, improving deliverability.

February 2025 - EasyDMARC
Marketer view

Email marketer from Reddit shares that when troubleshooting SPF failures, it's important to verify that all email sending sources are included in your SPF record. Overlooking a legitimate source will cause emails from that source to fail SPF checks.

December 2023 - Reddit

What the experts say
5Expert opinions

Troubleshooting DMARC failures effectively involves utilizing DMARC reporting tools and services to gain visibility into email streams and authentication results. Setting up a DMARC vendor provides dashboards and automated alerts for unauthorized sending sources. DMARC alignment, requiring both SPF and DKIM to pass and align with the domain in the 'From:' header, is crucial. Starting with a 'p=none' policy allows monitoring and identification of issues before enforcing stricter policies that could impact legitimate email delivery. DMARC reports can reveal previously unknown email sources.

Key opinions

  • DMARC Vendor: Implementing a DMARC vendor simplifies troubleshooting through reporting and dashboard features.
  • DMARC Alignment: Strict DMARC alignment, where both SPF and DKIM pass and align, is essential for successful authentication.
  • Monitoring Policy: Starting with a 'p=none' policy allows monitoring of email streams before enforcing stricter policies.
  • Unknown Sources: DMARC reporting can help identify previously unknown email sources.
  • DMARC Reports: DMARC Summary reports are key to finding and answering questions about authentication issues

Key considerations

  • Tool Investment: Investing in a DMARC vendor provides the necessary tools for effective monitoring and troubleshooting.
  • Strict Enforcement: Strict DMARC enforcement without proper alignment can lead to legitimate email being blocked.
  • Gradual Implementation: Implementing DMARC policies gradually allows for identification and resolution of issues before enforcing stricter measures.
  • Report Analysis: DMARC reports require careful analysis to identify underlying authentication issues.
Expert view

Expert from Word to the Wise explains to start with a DMARC policy of 'p=none' to monitor your email streams and identify any unauthorized sending sources before enforcing stricter policies. This allows time to correct any misconfigurations or authentication issues without impacting legitimate email delivery.

December 2022 - Word to the Wise
Expert view

Expert from Email Geeks mentions the benefit of DMARC reporting in identifying previously unknown email sources.

July 2023 - Email Geeks
Expert view

Expert from Email Geeks shares that implementing a DMARC vendor to capture reports and generate a dashboard is the best approach for troubleshooting DMARC issues. He recommends tools like Redsift, dmarcian, and EasyDMARC to identify mail streams and assess authentication implementation. He highlights the difficulty of troubleshooting without such tools and mentions how Redsift proactively alerted him to mail from other ESPs, automating the identification process.

August 2022 - Email Geeks
Expert view

Expert from Spam Resource explains that strict DMARC alignment is essential. Both SPF and DKIM must pass and be aligned with the domain in the 'From:' header. Misalignment, even with passing authentication, will cause DMARC failures.

February 2024 - Spam Resource
Expert view

Expert from Email Geeks explains that DMARC summary reports can answer questions about email authentication issues. He adds that DMARC is set up at the domain level, but every email source from that domain needs correct authentication, and the DMARC reports will identify unauthenticated sources.

April 2021 - Email Geeks

What the documentation says
5Technical articles

Troubleshooting DMARC failures involves understanding the underlying issues causing SPF and DKIM failures, analyzing DMARC reports, ensuring correct DMARC record syntax, validating DKIM signature verification, and practicing regular DKIM key rotation. SPF failures often stem from unauthorized sending server IPs, while DKIM failures can arise from signature verification problems. DMARC reports, both aggregate and forensic, provide insights into authentication results. A properly configured DMARC record with correct syntax is crucial. Regular DKIM key rotation enhances security by mitigating the risk of key compromise.

Key findings

  • SPF/DKIM Failures: DMARC failures often result from underlying SPF and DKIM authentication problems.
  • Report Analysis: DMARC reports (aggregate and forensic) provide critical data for diagnosing authentication issues.
  • Record Syntax: Correct DMARC record syntax, including the 'v', 'p', and 'rua' tags, is vital.
  • DKIM Verification: Proper DKIM signature verification, with correct alignment and key matching, is essential.
  • Key Rotation: Regular DKIM key rotation enhances security and limits the impact of potential compromises.

Key considerations

  • Authentication Issues: Addressing underlying SPF and DKIM failures is paramount for resolving DMARC issues.
  • Report Interpretation: Accurate interpretation of DMARC reports is crucial for identifying the root cause of failures.
  • Record Configuration: Careful configuration of the DMARC record is essential to avoid unintended consequences.
  • Security Practices: Implementing robust DKIM key rotation practices enhances overall email security.
  • Key Alignment: Double check that your DKIM 'd' and 's' tags are properly aligned
Technical article

Documentation from Dmarcian shares that DMARC reports are crucial for diagnosing authentication issues. Aggregate reports provide a summary of authentication results, while forensic reports offer detailed information about individual emails that failed authentication, aiding in pinpointing the source of the problems.

February 2023 - Dmarcian
Technical article

Documentation from Microsoft explains that issues with DKIM verification can cause DMARC failures. Ensuring that the DKIM signature is properly aligned with the 'd' and 's' tags, and that the public key used for verification matches the private key used for signing, is critical for successful authentication.

October 2022 - Microsoft
Technical article

Documentation from ReturnPath explains that regular DKIM key rotation is important for security. Using the same key for a prolonged period increases the risk of compromise. Rotating your DKIM keys ensures that even if a key is compromised, the impact is limited.

December 2022 - ReturnPath
Technical article

Documentation from RFC explains that a misconfigured DMARC record can lead to authentication failures. Ensuring the correct syntax, including the 'v', 'p', and 'rua' tags, is vital for proper DMARC implementation. Errors in the record can cause legitimate emails to be incorrectly flagged.

December 2021 - RFC 6376
Technical article

Documentation from Google Workspace Admin Help explains that DMARC failures can occur due to SPF failures, DKIM failures, or both. It elaborates on SPF failures happening when the sending server's IP address isn't authorized in the SPF record, and DKIM failures arising from issues with the DKIM signature verification process.

September 2023 - Google Workspace Admin Help