What are the steps to troubleshoot DMARC reject policy causing low email delivery rates after implementation?
Michael Ko
Co-founder & CEO, Suped
Published 2 May 2025
Updated 17 Aug 2025
6 min read
Implementing a DMARC reject policy is a crucial step for improving email security and deliverability. It tells receiving mail servers to outright reject emails that fail authentication, effectively preventing spoofing and phishing attacks using your domain. However, a common challenge arises when this policy leads to a sudden drop in legitimate email delivery rates.
This usually indicates that legitimate emails are failing DMARC authentication because their underlying SPF or DKIM records are not correctly configured or aligned. The immediate impact can be significant, ranging from low delivery rates to complete email blackholes, causing disruption to critical communications.
The core issue when moving directly to a p=reject policy without proper preparation is that any email failing DMARC authentication will be rejected by recipient mail servers. This isn't limited to malicious emails, but also includes legitimate emails sent from services or systems that haven't been correctly configured with SPF (Sender Policy Framework) or DKIM (DomainKeys Identified Mail), or where alignment has not been achieved.
Many organizations make the mistake of deploying a strict DMARC policy too quickly. A gradual rollout is strongly recommended, starting with a p=none policy to gather data, then moving to p=quarantine, and finally to p=reject. This phased approach allows you to identify and fix authentication issues for all legitimate sending sources before instructing recipients to reject failing emails. You can learn more about how to safely transition your DMARC policy to quarantine or reject.
Immediate action: Revert DMARC policy
If you've just implemented DMARC with a p=reject policy and are experiencing low delivery rates, the most critical immediate step is to change your DMARC record to p=none. This will tell receiving servers not to take any action on emails that fail DMARC, allowing them to deliver your emails while you troubleshoot. Here's an example of a DMARC record set to p=none:
Remember, this is a temporary measure to restore deliverability. The goal is to return to p=reject once all issues are resolved. For a deeper understanding of policy best practices, consult our guide on what are the best practices for setting DMARC policy.
Verifying your email authentication setup
The primary reason for DMARC reject policy causing low delivery rates is often a misconfiguration or lack of alignment with SPF and DKIM. DMARC relies on these two protocols to verify email authenticity. If either SPF or DKIM passes, and their respective domains align with the DMARC record's domain, the email passes DMARC.
To troubleshoot, you need to verify the SPF and DKIM records for all IP addresses and sending domains used by your organization. This includes your primary domain, subdomains, and any third-party services that send emails on your behalf (e.g., email service providers, CRM systems, marketing automation platforms). A common scenario is when your email service provider sends emails through their infrastructure, but the From address in the email header does not properly align with the SPF or DKIM domains used by that provider.
Checking your authentication involves inspecting the email headers of messages sent from your domain. Look for the Authentication-Results header to see the pass/fail status for SPF, DKIM, and DMARC. Crucially, check the domain alignment. We have a comprehensive guide on how to troubleshoot and fix SPF and DMARC settings.
You can use an online DMARC verification tool or send a test email to a dedicated analysis address to receive a detailed report on your email's authentication status. This will highlight specific failures and provide actionable insights. Ensure your SPF and DKIM records meet the requirements of major mailbox providers.
Analyzing DMARC reports
DMARC reports are essential for understanding your email ecosystem. They provide insights into which emails are passing or failing authentication and from which sources. There are two main types: aggregate reports (RUA) and forensic reports (RUF).
Aggregate reports provide XML summaries of email traffic that references your domain, including pass/fail rates for SPF and DKIM, and the DMARC policy applied. These reports are invaluable for identifying legitimate sending sources that might not be correctly authenticated. Forensic reports (if enabled) offer more detailed, anonymized information about individual failed emails, which can help pinpoint the exact cause of failure.
The rua tag in your DMARC record specifies the email address where aggregate reports are sent. Regularly analyzing these reports is key to diagnosing DMARC failures and their impact on email deliverability. For a step-by-step approach, refer to our guide on how to diagnose DMARC failures using DMARC reports.
DMARC Policy
Description
Impact on deliverability
p=none
Monitoring mode. Receiving servers collect data and send reports, but no action is taken on failing emails.
No direct impact on deliverability. Allows you to identify all sending sources.
p=quarantine
Receiving servers are instructed to treat failing emails suspiciously, often placing them in spam folders.
Emails might land in spam, reducing inbox placement. Use this once you're confident in most sending sources.
p=reject
Receiving servers are instructed to completely reject emails that fail DMARC authentication.
Failing emails will not be delivered at all, potentially causing severe delivery rate drops if misconfigured.
Common pitfalls and solutions
Low email delivery rates after implementing a DMARC reject policy often stem from common pitfalls. These include overlooking third-party sending services, incorrect SPF or DKIM DNS entries, or a lack of strict alignment between the From domain and the authenticated domains. This means that while your DMARC record might be correctly published, the underlying authentication mechanisms aren't covering all your legitimate email streams.
To address these, ensure every service that sends emails using your domain has proper SPF and DKIM setup. This might involve adding include mechanisms to your SPF record or configuring CNAME records for DKIM. The goal is to achieve DMARC alignment for all your email traffic. Remember, DMARC requires either SPF or DKIM to align with the From address.
Common problems
Premature DMARC reject: Implementing p=reject without prior monitoring and fixing issues.
Incomplete sender list: Not accounting for all legitimate third-party senders, leading to unauthenticated emails.
Alignment failures: SPF or DKIM passing, but the domains don't align with the From address.
Lack of monitoring: Not regularly checking DMARC reports to identify failing sources and authentication issues.
Effective solutions
Start with p=none:Begin with a p=none policy and use DMARC reports to discover all legitimate senders.
Configure all senders: Ensure every email sending service is correctly configured with SPF and DKIM. This is a critical step for your DMARC authentication protocol.
Use the pct tag: Gradually increase the percentage of emails to which the DMARC policy applies using the pct tag, slowly moving towards 100% reject.
Once you have addressed the underlying SPF and DKIM issues, you can gradually increase the enforcement level. Start with a small percentage using the pct tag (e.g., p=reject; pct=10;) and monitor your DMARC reports closely. As confidence grows, increase the percentage until you reach 100% enforcement.
Views from the trenches
Best practices
Always start DMARC with a p=none policy to gather comprehensive reports from all sending sources and identify unauthenticated email streams before enforcing stricter policies.
Thoroughly audit all services sending email on your behalf to ensure each has correct SPF and DKIM records and proper alignment with your DMARC domain.
Regularly monitor your DMARC aggregate reports to detect any new or recurring authentication failures and address them promptly.
Gradually transition your DMARC policy from p=none to p=quarantine and then to p=reject, using the 'pct' tag to slowly increase enforcement.
Ensure SPF and DKIM records are correctly published in your DNS and that the domains used for authentication align with your email's 'From' header.
Common pitfalls
Jumping straight to a p=reject DMARC policy without sufficient testing, leading to legitimate emails being blocked or sent to spam folders.
Neglecting to configure SPF and DKIM for all third-party email senders, such as marketing platforms, CRM systems, or transactional email services.
Not understanding DMARC alignment requirements, where the SPF/DKIM domains must match the primary domain in the 'From' address, not just pass authentication.
Failing to review DMARC reports regularly, which means authentication failures and potential spoofing attempts go unnoticed.
Ignoring the 'pct' tag and attempting to enforce a reject policy on 100% of emails without ensuring all legitimate traffic passes DMARC.
Expert tips
Verify your email authentication by sending a test email to an email analysis service to get an immediate detailed breakdown of SPF, DKIM, and DMARC passes or failures.
Consult with an email deliverability expert or your Email Service Provider's support team if you encounter persistent DMARC issues or need help interpreting complex reports.
Use DNS lookup tools to confirm that your DMARC, SPF, and DKIM records are correctly published and resolving as expected, especially after making changes.
Segment your DMARC implementation by subdomains, applying stricter policies to subdomains first while maintaining p=none on your root domain until fully compliant.
Prioritize fixing authentication for high-volume or critical email streams first, then address lower-volume senders, always verifying changes with DMARC reports.
Expert view
Expert from Email Geeks says that you do not go to a full reject policy before authenticating all your sources that send as the root domain.
2024-06-07 - Email Geeks
Expert view
Expert from Email Geeks says that if you didn't check your authentication before adding the DMARC record, you should change it immediately to p=none.
2024-06-07 - Email Geeks
Ensuring DMARC success
Troubleshooting low email delivery rates after implementing a DMARC reject policy requires a systematic approach. The immediate priority is to revert to a p=none policy to restore deliverability. Following this, the focus shifts to thoroughly verifying SPF and DKIM configurations for all sending sources, ensuring proper alignment with your DMARC domain.
Consistent analysis of DMARC aggregate reports will provide the necessary data to identify and resolve authentication failures. By taking a phased approach and addressing each issue methodically, you can successfully implement a DMARC reject policy without negatively impacting your legitimate email traffic, ultimately enhancing your domain's reputation and security posture.
