How to deal with a failing DMARC email authentication protocol?
Michael Ko
Co-founder & CEO, Suped
Published 10 Jul 2025
Updated 17 Aug 2025
6 min read
Discovering that your Domain-based Message Authentication, Reporting & Conformance (DMARC) email authentication protocol is failing can be a frustrating experience. It often raises immediate concerns about email deliverability and potential security vulnerabilities, like email spoofing and phishing attempts. The impact of a failing DMARC protocol extends beyond just security, directly influencing whether your emails reach their intended inboxes or end up in spam folders.
A common misconception arises when DMARC reports show fail results, even with a p=none policy in place. While these reports highlight authentication issues, a p=none policy instructs recipient servers not to take any action, so it might not immediately impact your deliverability. However, it's still a critical issue that needs addressing to ensure proper email authentication and to meet modern sender requirements, such as those from Google and Yahoo.
In this guide, I'll walk you through understanding why DMARC fails and the steps you can take to diagnose, fix, and ultimately enhance your email security and deliverability. We'll explore the nuances of DMARC policies, common pitfalls, and practical solutions.
DMARC works by building on two foundational email authentication protocols: Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM). For a DMARC check to pass, an email must pass either SPF or DKIM authentication, and critically, the domains used in these checks must align with the From header (the domain visible to the recipient).
A DMARC failure often means that your email is not properly authenticated as your own domain, even if it's sent via a legitimate email service provider (ESP). This is known as an alignment failure. For instance, if your ESP signs emails with their domain and not yours, DMARC might report a failure, even if SPF or DKIM technically passed for the ESP's domain. Understanding the concept of DMARC alignment is crucial to troubleshooting.
The DMARC policy itself dictates how recipient mail servers should handle emails that fail authentication and alignment. The three main policy options are:
p=none: This monitoring-only policy provides visibility into DMARC failures without impacting deliverability. It's often the starting point for DMARC implementation.
p=quarantine: Emails failing DMARC are sent to the recipient's spam or junk folder.
p=reject: Emails failing DMARC are blocked entirely and not delivered.
Diagnosing DMARC issues with reports
The first step in dealing with a DMARC failure is to accurately diagnose its cause. This primarily involves analyzing DMARC reports. There are two types: aggregate reports (RUA) and forensic reports (RUF).
Aggregate reports provide a high-level overview of email traffic for your domain, showing which emails pass or fail DMARC, SPF, and DKIM, and from which IP addresses. These reports are invaluable for identifying legitimate sending sources that might not be properly authenticated. To receive these reports, your DMARC record needs to include a rua tag with an email address for receiving reports. There are many DMARC reporting tools that can help you parse these XML reports into an understandable format.
Here's an example of a DMARC record that includes a rua tag for aggregate reports:
Forensic reports, while providing more detailed information about individual failed emails, are less commonly used due to privacy concerns and the potential for large volumes. Analyzing these reports is key to understanding why your DMARC is failing, especially when your email authentication seems correct.
Common causes and fixes for DMARC failures
Once you've analyzed your DMARC reports, you'll likely identify common issues causing failures. These often revolve around misconfigurations of SPF, DKIM, or a lack of proper alignment for all your sending sources. The goal is to ensure that every legitimate email sent from your domain passes both SPF and DKIM authentication with proper alignment.
One frequent culprit is when DKIM from a domain mismatch occurs, or when SPF records are incorrectly set up. Another challenge can be handling email forwarding, which can break SPF authentication. This table highlights some common issues and their solutions:
Common cause of DMARC failure
Solution
SPF permerror (too many DNS lookups)
Consolidate or flatten your SPF record to stay within the 10 DNS lookup limit.
DKIM alignment failure with third-party senders
Ensure your third-party ESPs are signing emails with your domain or that you've configured a custom sending domain.
Incorrect DMARC record syntax
Verify your DMARC record's TXT entry for typos or incorrect tags using a DMARC record generator or checker.
Subdomain email sending issues
Ensure SPF and DKIM are properly configured for each subdomain you use to send emails.
The key is to systematically go through your sending sources, ensure they are all authorized in your SPF record, and that DKIM is correctly configured and aligned for each. This may involve working closely with your email service providers (ESPs) or marketing platforms to ensure they sign emails with your domain.
Moving towards DMARC enforcement
Once you've identified and fixed the underlying authentication and alignment issues, the next step is to progress your DMARC policy from p=none to an enforcement policy like p=quarantine or p=reject. This transition should be done gradually and with continuous monitoring.
Moving to p=quarantine is usually the next logical step. It allows you to monitor the impact of DMARC enforcement without completely blocking emails. After a period of monitoring and ensuring legitimate emails are not being miscategorized, you can then consider moving to p=reject. This provides the highest level of protection against email spoofing and phishing.
Best practices for DMARC enforcement
Start with p=none: Begin by implementing DMARC with a p=none policy to gather data and identify all legitimate sending sources.
Analyze reports regularly: Use DMARC aggregate reports to continuously monitor your email ecosystem and ensure compliance.
Gradual enforcement: Incrementally move your policy from p=none to p=quarantine, then to p=reject as you achieve full compliance.
Always start DMARC with a 'p=none' policy to monitor email traffic and identify legitimate sending sources without affecting deliverability.
Consistently analyze DMARC aggregate reports to understand authentication failures and ensure all your legitimate email senders are correctly configured for SPF and DKIM alignment.
Gradually transition your DMARC policy from 'p=none' to 'p=quarantine' and then to 'p=reject' while closely monitoring your deliverability and reports to prevent legitimate emails from being blocked.
Ensure that all third-party email service providers you use are correctly configured to send emails on behalf of your domain, including proper DKIM signing and SPF inclusion.
Common pitfalls
Implementing a 'p=reject' DMARC policy too quickly without thorough testing, which can lead to legitimate emails being rejected and significant deliverability issues.
Failing to monitor DMARC reports regularly, which means you might miss critical authentication failures or unauthorized use of your domain.
Ignoring DMARC alignment, particularly when using third-party senders, leading to emails failing DMARC even if SPF and DKIM pass.
Having an SPF record with too many DNS lookups (over 10), causing SPF 'permerror' and subsequent DMARC failures, affecting deliverability.
Expert tips
Use a DMARC reporting tool to simplify the analysis of complex XML aggregate reports into actionable insights, making it easier to pinpoint and resolve authentication issues.
Prioritize fixing DKIM alignment issues over SPF, especially for third-party senders, as DKIM is more resilient to forwarding and is a key factor for DMARC pass rates.
If you're a bulk sender, prioritize achieving DMARC enforcement to comply with new requirements from major mailbox providers like Google and Yahoo, which mandate strict authentication.
Regularly check your DMARC record's syntax and DNS publication to ensure it is always correct and accessible to receiving mail servers, preventing unexpected failures.
Marketer view
Marketer from Email Geeks says to sign up for a DMARC reporting tool and begin collecting reports to properly authenticate and align any failing sources.
2024-07-25 - Email Geeks
Marketer view
Marketer from Email Geeks says to determine if the DMARC issue is a failure or a lack of implementation; if it's a failure, identify and fix the root cause, and consider monitoring DNS to detect future issues faster.
2024-07-25 - Email Geeks
The path to DMARC enforcement
Dealing with a failing DMARC email authentication protocol can seem daunting, but it's a critical step towards securing your email communication and ensuring optimal deliverability. By understanding the nuances of DMARC, leveraging its reporting features, and systematically addressing authentication and alignment issues, you can transition your domain to an enforced DMARC policy.
This proactive approach not only protects your domain from malicious activities like spoofing and phishing but also significantly improves your email deliverability rates, ensuring your messages consistently reach the inbox. Remember, a robust DMARC implementation is a continuous process of monitoring and refinement.
