When you notice a sudden drop in your DMARC authentication rate, it can be quite alarming. DMARC, or Domain-based Message Authentication, Reporting and Conformance, is crucial for protecting your domain from unauthorized use, such as phishing and spoofing. It tells receiving mail servers what to do with messages that fail authentication, usually based on SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) checks. A decline in this rate means a higher percentage of emails purporting to be from your domain are no longer passing these vital security checks, potentially leading to increased spam classifications or outright rejection by recipients.
Such a drop can significantly impact your email deliverability, as major mailbox providers like Google and Yahoo are increasingly stringent about email authentication. If your DMARC pass rate is suddenly falling, it indicates underlying issues that need immediate attention. These issues can range from simple misconfigurations to more complex problems involving unauthorized senders or changes in how email is being routed or processed.
Investigating the cause requires a systematic approach, often starting with DMARC reports, which provide valuable insights into why emails are failing authentication. Without these reports, pinpointing the exact problem can be like looking for a needle in a haystack. Understanding the potential reasons behind such a drop is the first step toward diagnosing and resolving the problem, ensuring your legitimate emails continue to reach their intended recipients.
A sudden drop in your DMARC authentication rate almost always points to an issue with how emails are being sent from your domain, or how your authentication records are configured. DMARC relies on SPF and DKIM to pass, along with alignment checks. If either SPF or DKIM fails to align with your sending domain, DMARC will fail. The primary culprit for a sudden decline is often a change in your sending infrastructure that hasn't been properly authenticated.
This could mean a new email service provider (ESP) or third-party sending service was integrated without updating your SPF record to include their IP addresses or domains, or without configuring DKIM signing correctly. It's common for different departments within a company to adopt new services without central IT or marketing being aware, leading to emails being sent from unauthenticated sources. Since DMARC leverages both SPF and DKIM, a misconfiguration in either can directly lead to DMARC authentication failures.
Another factor could be changes in your DMARC record itself. If you recently updated your DMARC policy from p=none to a stricter p=quarantine or p=reject, this could expose previously hidden authentication failures. When your policy is at p=none, receiving servers simply report failures without taking action. A stricter policy, however, will cause these previously ignored failures to be reflected as a drop in your authentication rate.
Common causes of DMARC authentication drops
One of the most frequent causes for a sudden dip is the introduction of new, unauthenticated sending sources. Imagine a new marketing tool or a support platform starts sending emails on your behalf. If their sending IPs or domains aren't added to your SPF record, or if DKIM isn't correctly configured for them, those emails will likely fail DMARC authentication. This is a common pitfall, especially in larger organizations where various departments might use different email services.
Another cause is misconfiguration of existing SPF or DKIM records. Even a small typo in your DNS records, an expired DKIM key, or exceeding the 10-lookup limit for SPF can lead to authentication failures. DNS propagation delays after a change can also temporarily affect your DMARC rate. Additionally, if there's a surge in legitimate emails being forwarded, DMARC may fail because the forwarded message can break SPF or DKIM, causing the original authentication to be lost without ARC (Authenticated Received Chain) being properly implemented.
Finally, an increase in spoofing attempts can also cause your DMARC failure rate to rise. While DMARC is designed to block (or quarantine) these fraudulent emails, they still count as DMARC failures on your reports. A sudden increase in unauthorized emails attempting to spoof your domain could show up as a drop in your legitimate DMARC pass rate, even if your own sending practices are sound. This is where DMARC reports become invaluable in distinguishing between legitimate failures and malicious activity.
How to diagnose a drop in DMARC authentication
The most effective way to diagnose a drop in DMARC authentication is to analyze your DMARC aggregate reports (RUA). These XML reports provide a comprehensive overview of your email traffic, detailing which sources are sending on your behalf, their authentication results (SPF, DKIM, DMARC), and the actions taken by receiving mail servers. Look for sudden increases in emails failing authentication, new unlisted sending IP addresses, or changes in how legitimate senders are authenticating. You can also monitor Google Postmaster Tools for trends in your authentication rates, spam complaints, and domain reputation.
If you don't have DMARC reporting set up, that should be your first step. It provides the visibility needed to understand your email ecosystem. Without DMARC reports, you're essentially flying blind. For specific issues, you might need to check your DNS records for SPF and DKIM entries. Use a DNS checker tool to ensure your SPF record is valid, doesn't exceed the 10-lookup limit, and includes all authorized sending IPs. For DKIM, verify that the public key in your DNS matches the private key used by your sending service and that the selector is correct.
Investigating the drop
Review DMARC reports: Look for specific IP addresses or sending sources that are failing DMARC. These reports will tell you which senders are causing the problem.
Check recent changes: Were any new email sending platforms or third-party services recently onboarded?
Examine DNS records: Verify your SPF, DKIM, and DMARC records for any errors, typos, or recent, unauthorized changes.
Preventing future DMARC authentication issues
To prevent future drops in DMARC authentication, a proactive and systematic approach to email security is essential. Firstly, always use DMARC reports. They are your eyes and ears in the email ecosystem, alerting you to issues before they escalate. Regularly review these reports, looking for anomalies like new unauthenticated senders or spikes in failed authentication attempts. Monitoring helps you understand why your DMARC success rate fluctuates.
Implement a clear process for onboarding new email sending services or vendors. Before any new service starts sending on behalf of your domain, ensure their SPF and DKIM configurations are correctly set up and tested. This includes updating your domain's DNS records appropriately. A centralized system for managing all email sending sources can help prevent rogue senders from impacting your authentication rates.
Gradually enforce your DMARC policy. Starting with p=none (monitoring mode) allows you to gather data and identify all legitimate sending sources without impacting deliverability. Once you have a clear picture, you can then safely transition to p=quarantine, and eventually p=reject. This phased approach minimizes the risk of inadvertently blocking legitimate email. Also, regularly check if your domain is listed on any email blocklists (or blacklists), as a listing can affect how receivers treat your emails, even if DMARC technically passes.
Restoring your DMARC authentication rate
Once you've identified the root cause of the DMARC authentication drop, addressing it promptly is crucial. If the issue is a new, unauthenticated sending source, the immediate fix involves updating your SPF record to include the new IP address or domain of the service, or configuring DKIM signing for that service. Ensure proper alignment for both SPF and DKIM records to ensure they pass DMARC.
For misconfigurations in existing DNS records, correct them immediately. Double-check for typos, ensure SPF records do not exceed the 10-lookup limit, and verify that DKIM keys are current and correctly published. Remember that DNS changes can take some time to propagate globally (up to 48 hours), so monitor your DMARC reports and Postmaster Tools data for the improvements to reflect. If you suspect an increase in spoofing, your DMARC reports will confirm this by showing failed attempts from unauthorized IP addresses.
The key is continuous monitoring and verification. Don't set up DMARC and forget about it. Regularly reviewing your DMARC reports (RUA and RUF for forensic details) will help you catch issues early. It also allows you to refine your DMARC policy over time, eventually moving to a stricter p=reject policy once you are confident that all legitimate email traffic is properly authenticated. This iterative process is vital for maintaining high DMARC authentication rates and protecting your domain's integrity.
Views from the trenches
Best practices
Always monitor your DMARC aggregate reports to quickly spot any drops or anomalies in authentication rates.
Maintain an up-to-date inventory of all email sending services and applications used across your organization.
Ensure SPF and DKIM are correctly configured and aligned for every legitimate email sending source.
Implement a phased rollout for DMARC policy enforcement, starting with p=none before moving to stricter policies.
Regularly check your domain’s reputation and actively monitor for any blocklist (or blacklist) listings.
Common pitfalls
Onboarding new SaaS email senders without updating SPF records or configuring DKIM.
Not regularly checking DMARC reports, leading to delayed detection of authentication issues.
Setting a p=reject DMARC policy too early without comprehensive monitoring and understanding.
Ignoring DMARC failure reports, allowing spoofing or misconfigurations to persist.
Making DNS changes without verifying their impact on email authentication and propagation.
Expert tips
Leverage DMARC forensic reports (RUF) for detailed insights into individual email failures, if privacy concerns allow.
Consider using an email authentication testing tool to validate SPF, DKIM, and DMARC configurations before deployment.
Educate internal teams about the importance of DMARC compliance when introducing new email sending tools.
Automate DMARC report processing with a DMARC monitoring solution to simplify analysis and alerts.
Pay close attention to DMARC alignment, not just SPF and DKIM pass rates, as alignment is key.
Marketer view
Marketer from Email Geeks says they observed a 7% drop in DMARC authentication in Postmaster Tools since February, seeking troubleshooting advice.
2020-02-19 - Email Geeks
Expert view
Expert from Email Geeks says DMARC reports are essential for understanding the reasons behind authentication drops and provide a clearer picture.
2020-02-19 - Email Geeks
Rebuilding your email sender reputation
A drop in DMARC authentication is a clear signal that something has changed within your email sending infrastructure or that your domain is being targeted for spoofing. Addressing this quickly is vital for maintaining your sender reputation and ensuring your emails reach the inbox. By diligently monitoring your DMARC reports, meticulously managing your SPF and DKIM records, and being proactive about authenticating all legitimate sending sources, you can effectively mitigate drops in DMARC authentication and protect your domain from unauthorized use. This commitment to proper email authentication not only secures your brand but also contributes to better overall deliverability for your email campaigns.
