Summary
A decreasing DMARC success rate is often caused by a combination of factors related to SPF, DKIM, and email sending practices. Common issues include misconfigured or changed SPF records (especially exceeding DNS lookup limits), problems with DKIM signatures (such as key rotation or tampering), and using third-party email services without proper SPF/DKIM setup. Additionally, email forwarding can break SPF authentication, and a changed 'From' address can cause alignment issues. Regularly monitoring and analyzing DMARC reports is crucial for identifying and addressing these problems. Also, even with a 'p=none' policy, some regional providers might still treat it as a reject. Starting with a p=none policy when first implementing dmarc to monitor the impact before enforcing stricter policies is advised.
Key findings
- SPF/DKIM Configuration: Incorrect SPF records, exceeding DNS lookup limits, and invalid DKIM signatures are common causes.
- Alignment Issues: Mismatched 'From' address can cause SPF/DKIM to pass but fail DMARC alignment.
- Third-Party Services: Improper SPF/DKIM setup for third-party email services leads to failures.
- Forwarding Problems: Email forwarding often breaks SPF authentication.
- Importance of Reports: DMARC reports are essential for diagnosing failure reasons and identifying non-compliant emails.
- DMARC Policy Enforcement: Strict DMARC policies (quarantine/reject) can negatively impact deliverability.
- Regional Provider Variations: Even with a p=none policy, some regional providers may treat it as p=reject.
Key considerations
- Review SPF/DKIM Settings: Ensure accurate SPF records within DNS limits and valid DKIM signatures.
- Monitor DMARC Reports: Regularly analyze DMARC reports to identify issues.
- Configure Third-Party Services: Verify correct SPF/DKIM setup for all third-party senders.
- Assess Forwarding Impact: Understand how forwarding affects SPF and consider alternatives.
- Start with Monitoring: Begin with 'p=none' to monitor impact before stricter enforcement.
- Address Alignment Issues: Ensure SPF and DKIM domains align with the From: domain.
- Unauthorized Sending: Identify and prevent unauthorized sending of email from your domain.
What email marketers say
11 marketer opinions
A decreasing DMARC success rate can stem from various interconnected factors related to SPF, DKIM, and email sending practices. The most frequently mentioned causes involve misconfigurations or changes in SPF records (including exceeding DNS lookup limits), issues with DKIM signatures (such as key rotation problems or tampering), and the use of third-party email services without proper SPF/DKIM setup. Forwarding can also break SPF, leading to failures. Consistently monitoring DMARC reports is essential for diagnosing and addressing these issues, as these reports pinpoint the exact reasons for DMARC failure.
Key opinions
- SPF/DKIM Issues: Incorrectly configured SPF records, DKIM signature problems (e.g., key rotation, tampering), or exceeding the SPF DNS lookup limit are frequent causes.
- Alignment Problems: Changes to the 'From' address can cause SPF and DKIM to pass but fail alignment, leading to DMARC failures.
- Third-Party Services: Using third-party email services without proper SPF/DKIM configuration is a common reason for failure.
- Forwarding Issues: Email forwarding can break SPF authentication, causing DMARC to fail.
- Unauthorized Sending: Unauthorized email sending from your domain is a cause for DMARC failing.
- Monitoring is Key: DMARC reports are crucial for diagnosing the root cause of DMARC failures and should be regularly monitored.
Key considerations
- Review SPF/DKIM Setup: Ensure your SPF records are accurate and within DNS lookup limits, and that DKIM signatures are valid.
- Monitor DMARC Reports: Regularly analyze DMARC reports to identify failing sources and reasons for failure.
- Check Third-Party Integrations: Verify that any third-party email services are properly configured with SPF and DKIM.
- Consider Forwarding Impact: If forwarding is common, understand how it affects SPF and consider alternative solutions.
- Infrastructure Changes: When making changes to your email infrastructure, ensure SPF and DKIM are correctly configured for the new servers or services.
- DMARC Policy Enforcement: Be aware that even with a 'p=none' policy some regional providers can treat is as reject.
Marketer view
Email marketer from EmailSecuritySPF forum responds that DMARC failures are often linked to improperly configured SPF records (especially exceeding the 10 DNS lookup limit) or broken DKIM signatures due to modifications during transit. Using a DMARC monitoring tool is recommended.
12 Feb 2025 - EmailSecuritySPF Forum
Marketer view
Email marketer from EasyDMARC explains that common reasons for DMARC failure are changes in email sending practices, problems with SPF records, issues with DKIM signatures, and unauthorized email sending from your domain.
18 Dec 2021 - EasyDMARC
What the experts say
4 expert opinions
DMARC failures are often linked to forwarding issues, which break SPF. Analyzing DMARC reports is essential to pinpoint specific failure reasons and identify non-compliant emails. Enforcing DMARC policies (quarantine or reject) can impact deliverability, so starting with a monitoring-only policy (p=none) is recommended.
Key opinions
- DMARC Reports are Key: DMARC reports provide detailed information on failing emails and their causes, making them essential for diagnosis.
- Forwarding Impacts SPF: Email forwarding often breaks SPF authentication, leading to DMARC failures.
- Policy Enforcement Effects: Strict DMARC policies (quarantine/reject) can negatively impact deliverability if failures occur.
Key considerations
- Analyze DMARC Reports: Regularly parse and understand aggregate DMARC reports to identify and address issues.
- Assess Forwarding Impact: If forwarding is common, consider its effect on SPF and explore alternative solutions.
- Start with Monitoring: Begin with a 'p=none' DMARC policy to monitor the impact before enforcing stricter policies.
Expert view
Expert from Word to the Wise explains that DMARC issues often arise when emails are forwarded, as forwarding can break SPF. He suggests that if a significant portion of your email stream is forwarded, DMARC might cause deliverability problems. He also suggests to not use DMARC if you are a forwarder.
8 Dec 2023 - Word to the Wise
Expert view
Expert from Word to the Wise responds that if your DMARC policy is set to quarantine or reject, then failing DMARC can directly impact your deliverability. He recommends starting with a 'p=none' policy to monitor the impact before enforcing stricter policies.
11 Mar 2022 - Word to the Wise
What the documentation says
4 technical articles
DMARC failures occur primarily due to issues with SPF and DKIM authentication, including SPF failing to authenticate the sending server (often due to forwarding or misconfigured records) or DKIM signatures being invalid or absent. A crucial aspect is alignment – SPF and DKIM domains must align with the 'From:' domain. Monitoring aggregate DMARC reports helps pinpoint these issues.
Key findings
- SPF Authentication Failures: SPF failing to authenticate sending servers due to forwarding or misconfigured records is a common cause.
- DKIM Signature Problems: Invalid or absent DKIM signatures contribute to DMARC failures.
- Alignment Requirements: SPF and DKIM domains must align with the 'From:' domain for DMARC to pass.
- Importance of DMARC Reports: Aggregate DMARC reports are crucial for identifying the sources of DMARC failures.
Key considerations
- Review SPF Configuration: Ensure SPF records are correctly configured and include all authorized sending IPs.
- Validate DKIM Signatures: Confirm that DKIM signatures are valid and match the domain.
- Enforce Alignment: Verify that SPF and DKIM domains align with the 'From:' domain.
- Monitor DMARC Reports: Regularly examine aggregate DMARC reports to detect and address DMARC failures.
Technical article
Documentation from RFC7489 defines DMARC and explains that policy application depends on SPF and DKIM authentication results. Failures can occur when SPF or DKIM checks fail, or when the 'From:' domain does not align with the SPF or DKIM domains.
22 Dec 2022 - RFC Editor
Technical article
Documentation from Microsoft explains that DMARC failures can happen when emails are sent from IPs not included in the SPF record, or when DKIM signatures don't match the domain. Monitoring DMARC reports helps identify these issues.
14 Oct 2023 - Microsoft Documentation
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