How to identify and handle spoofed emails violating DMARC policies?
Michael Ko
Co-founder & CEO, Suped
Published 5 May 2025
Updated 16 Aug 2025
9 min read
Email spoofing is a prevalent tactic used by cybercriminals to deceive recipients by forging the sender's address. These malicious emails often appear to originate from legitimate sources, such as your own domain, a trusted business partner, or a well-known organization. The goal is to trick individuals into revealing sensitive information, clicking on malicious links, or performing unauthorized actions. This type of attack severely compromises trust and can lead to significant financial and reputational damage for businesses.
Domain-based Message Authentication, Reporting, and Conformance (DMARC) is a critical email authentication protocol designed to combat such spoofing attempts. It works by giving domain owners the ability to tell receiving mail servers how to handle emails that fail authentication checks. This includes specifying policies like p=none, p=quarantine, or p=reject.
The challenge lies in effectively identifying and handling these spoofed emails that violate your DMARC policies. While DMARC provides the framework, understanding its reports and taking appropriate actions is essential to protect your brand reputation and ensure email deliverability. This guide will walk you through the process, from understanding DMARC's foundational role to interpreting violation reports and implementing effective countermeasures.
Understanding DMARC and its role in spoofing prevention
DMARC builds upon two established email authentication protocols: Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM). SPF allows domain owners to publish a list of authorized IP addresses that can send emails on their behalf. DKIM, on the other hand, provides a cryptographic signature that verifies the sender's identity and ensures the email content has not been tampered with in transit. Both SPF and DKIM aim to prevent unauthorized use of a domain, but they have limitations when used independently.
DMARC brings these two together by adding a crucial layer of policy and reporting. It specifies how recipient mail servers should handle emails that fail SPF or DKIM checks and, importantly, provides a mechanism for domain owners to receive feedback on email authentication results. This feedback, primarily through DMARC reports, is key to identifying who is trying to send emails from your domain without authorization. You can learn more about the fundamentals of DMARC and its operation.
The power of DMARC lies in its policy enforcement. When you implement a DMARC record, you tell the world how to treat emails purporting to be from your domain but failing authentication. This policy is set using the 'p' tag in your DMARC record. A p=none policy monitors activity without taking action, while p=quarantine instructs servers to place unauthenticated emails in spam folders. The strongest policy, p=reject, tells recipient servers to block (reject) emails that fail authentication entirely. This progressive enforcement is critical for brand protection. For more information, read our guide on safely transitioning your DMARC policy.
Identifying spoofed emails through DMARC reports
The most effective way to identify spoofed emails violating DMARC policies is by analyzing DMARC reports. There are two primary types of reports: aggregate reports (RUA) and forensic reports (RUF). Aggregate reports provide an overview of all email traffic originating from your domain, showing which messages passed or failed authentication, and by whom. Forensic reports, while less common due to privacy concerns, offer more detailed information about individual failed messages.
To receive these reports, your DMARC record must include the rua tag with an email address where the reports should be sent. Here's an example of how a DMARC record might look, including the reporting address:
Once you start receiving these reports, you will see data from various mailbox providers (like Google, MicrosoftYahoo). These reports contain XML files that can be complex to parse manually. Specialized DMARC monitoring services can help you visualize this data, making it easier to pinpoint unusual sending patterns or unauthorized senders. Look for source IP addresses that are not part of your legitimate sending infrastructure, domains that are not yours but are trying to send emails using your domain, and significant volumes of emails failing DMARC authentication. To help you diagnose these failures, check out our guide on diagnosing DMARC failures using DMARC reports.
A common sign of spoofing (or a potential misconfiguration) is a high percentage of emails failing DMARC authentication, particularly from unknown IP addresses or services. If SPF and DKIM authentication both fail, DMARC will trigger its policy. The reports will show you the exact domains and IP addresses attempting to spoof your identity. Pay close attention to source IP addresses and the disposition (what action the receiver took based on your DMARC policy), which indicates how many messages were rejected or quarantined. To get a better sense of common DMARC fields, check out the following table:
Field
Description
Source IP
The IP address from which emails claiming to be from your domain were sent.
Count
Number of emails from that source IP for your domain.
Disposition
The action taken by the receiving server (none, quarantine, reject).
SPF Result
Indicates if SPF passed or failed for the email.
DKIM Result
Indicates if DKIM passed or failed for the email.
Alignment
Shows if the 'From' domain aligned with SPF and DKIM authenticated domains.
If you are struggling with a high volume of DMARC failures and cannot identify the legitimate senders from your reports, it might be due to a misconfigured DMARC record or issues with your authorized sending sources. To learn more about identifying email sending vendors, refer to our comprehensive guide on identifying email sending vendors.
Handling DMARC violations and mitigating spoofing
Once you've identified instances of spoofing through your DMARC reports, the next step is to take action. The approach varies depending on your DMARC policy and the nature of the spoofing. If you're on a p=none policy, your primary action will be to move towards a stricter policy like quarantine or reject. This requires careful planning and ensuring all legitimate email sources are properly authenticated with SPF and DKIM. Incorrect configuration can lead to legitimate emails being blocked or sent to spam.
For specific spoofing incidents, especially if they involve known malicious IP addresses, you might consider reporting the abuse. You can often find abuse contact information for IP addresses through regional internet registries (RIRs) like ARIN. While reporting might not stop all attacks, it can contribute to a safer internet ecosystem by flagging malicious actors. The primary way to mitigate damage from email spoofing is to ensure your domain is protected. Read our guide to mitigating damage from email spoofing.
If you already have a p=reject policy in place, then the DMARC system is working as intended, and violating emails should be blocked. However, it's still good practice to monitor reports for patterns or spikes in attempted spoofing, as this might indicate a targeted attack. Continuous monitoring helps you stay proactive. For more details, consult our article on how to use DMARC p=reject to combat email spoofing.
Before raising DMARC policy
Audit all senders: Ensure every service or application sending email on your behalf is authorized.
Verify SPF and DKIM: Confirm all legitimate senders are properly configured with SPF and DKIM.
Monitor reports: Analyze DMARC reports thoroughly to ensure no legitimate traffic is failing authentication.
Finally, understanding the differences between a blacklist and a blocklist can be beneficial, as email spoofing often leads to IP or domain listings. Staying informed on these topics can provide additional layers of defense against malicious actors and protect your email sender reputation. If your domain is spoofed, you can read more about what to do when your domain is spoofed. To prevent email from going to spam, check out this guide on how to combat fake emails.
Views from the trenches
Best practices
Implement SPF and DKIM authentication for all email sending services.
Use DMARC aggregate reports regularly to monitor email traffic and identify unauthorized senders.
Gradually move your DMARC policy from 'none' to 'quarantine' and then to 'reject' after thorough testing.
Ensure all legitimate email senders are accounted for and properly authenticated before enforcing stricter policies.
Common pitfalls
Setting a DMARC 'reject' policy without sufficient monitoring, leading to legitimate emails being blocked.
Ignoring DMARC reports, thus missing critical information about spoofing attempts or authentication issues.
Failing to update SPF or DKIM records when adding new email sending services, causing DMARC failures.
Not understanding that DMARC primarily protects your domain, not necessarily the display name.
Expert tips
Use a DMARC reporting tool to simplify report analysis and visualize data effectively.
Investigate any unknown IP addresses in DMARC reports using ARIN or other WHOIS databases to identify the source.
Keep security and support teams informed about potential increases in phishing attempts if your domain is being heavily spoofed.
Consider third-party DMARC management services for complex email environments.
Marketer view
Marketer from Email Geeks says they have seen a significant increase in emails violating their DMARC policy and are looking for ways to identify the unauthorized senders.
2021-11-19 - Email Geeks
Marketer view
Marketer from Email Geeks mentioned that if you have the IP addresses of the senders, you can perform an ARIN search to find the owner and their abuse contacts.
2021-11-19 - Email Geeks
Closing thoughts
Email spoofing remains a significant threat, but DMARC provides a powerful defense mechanism. By properly implementing and monitoring your DMARC policies, you gain visibility into who is attempting to send emails using your domain, whether authorized or not. This insight is invaluable for protecting your brand, maintaining trust with your recipients, and ensuring your legitimate emails reach their intended inboxes.
The key to effective DMARC management is not just setting up the record, but actively analyzing the reports to identify and address violations. This proactive approach allows you to detect unauthorized sending sources, improve your email authentication posture, and ultimately move towards a stricter DMARC policy with confidence. Remember that email security is an ongoing process, requiring continuous vigilance and adaptation.
Embracing DMARC as a cornerstone of your email security strategy will significantly reduce your exposure to phishing and spoofing attacks. It's an investment in your brand's integrity and the deliverability of your communications. Continuously review your DMARC reports, adjust your policies as needed, and ensure all your legitimate email streams are authenticated to build a robust defense against evolving threats.
Google, 
Microsoft
Yahoo). These reports contain XML files that can be complex to parse manually. Specialized DMARC monitoring services can help you visualize this data, making it easier to pinpoint unusual sending patterns or unauthorized senders. Look for source IP addresses that are not part of your legitimate sending infrastructure, domains that are not yours but are trying to send emails using your domain, and significant volumes of emails failing DMARC authentication. To help you diagnose these failures, check out our guide on diagnosing DMARC failures using DMARC reports.
