How can I use DMARC to prevent spammers from using my domain?
Michael Ko
Co-founder & CEO, Suped
Published 19 May 2025
Updated 17 Aug 2025
8 min read
Email spoofing, where spammers or phishers send emails that appear to originate from your domain, is a persistent threat. It can severely damage your brand reputation, lead to customer distrust, and even result in your legitimate emails being blocked or blacklisted (or blocklisted). The good news is that there's a powerful email authentication standard specifically designed to combat this: DMARC (Domain-based Message Authentication, Reporting & Conformance).
By implementing DMARC, you gain control over how receiving mail servers handle emails that claim to be from your domain but fail authentication checks. It's a critical step in protecting your domain from unauthorized use and ensuring your messages consistently reach the inbox.
In this guide, I'll walk you through how DMARC works and how to leverage it effectively to prevent spammers from exploiting your domain, safeguarding your email ecosystem and improving your overall email deliverability.
At its core, DMARC allows domain owners to tell receiving email servers what to do with messages that fail SPF (Sender Policy Framework) or DKIM (DomainKeys Identified Mail) authentication. Without DMARC, even if SPF and DKIM are set up, a receiving server might still accept spoofed emails, as there's no explicit instruction on how to handle failures. DMARC closes this gap, providing clear guidelines for message disposition.
DMARC works by establishing a policy that tells email receivers whether to allow, quarantine, or reject messages that don't pass authentication and alignment checks. Alignment is key, meaning the domain in the From header (the one users see) must align with the domain that passed SPF or DKIM. If a message fails these checks, DMARC instructs the receiving server on how to act, thereby preventing spammers from impersonating your domain.
For DMARC to function effectively, you must have SPF and DKIM records properly configured for your domain. These are the foundational authentication protocols. SPF specifies which mail servers are authorized to send email on behalf of your domain, while DKIM adds a digital signature to outgoing emails, allowing receivers to verify that the message hasn't been tampered with and truly originated from your domain. Together, these three records form a robust defense against email fraud. You can learn more about DMARC, SPF, and DKIM in our detailed guide.
How DMARC, SPF, and DKIM work together
SPF: Specifies which IP addresses are authorized to send email for your domain.
DKIM: Provides a digital signature to verify the message integrity and sender identity.
DMARC: Instructs receiving servers on what to do if SPF or DKIM fail (e.g., quarantine, reject) and provides reporting.
Setting up your DMARC record
To implement DMARC, you need to add a DMARC DNS TXT record to your domain. This record defines your policy and specifies where you want to receive DMARC reports. It's crucial to start with a cautious approach and gradually move to stricter policies to avoid disrupting legitimate email flow. Many organizations begin with a policy of p=none, which monitors email activity without affecting delivery, allowing you to collect data and identify all legitimate sending sources.
Once you've analyzed your DMARC reports and confirmed that all your legitimate email senders (including third-party services like marketing platforms or CRMs) are properly authenticating and aligning, you can then move to a p=quarantine policy. This instructs receiving servers to place unauthenticated emails from your domain into the recipient's spam or junk folder. The final and most protective step is to implement a p=reject policy, which tells receiving servers to reject these emails outright, preventing them from ever reaching the recipient's inbox. This policy is the strongest defense against spammers and spoofing. We have a detailed guide on how to safely implement DMARC p=reject.
Remember, the goal is to reach a p=reject policy, as this offers the highest level of protection against domain misuse. However, a rushed implementation can lead to legitimate emails being marked as spam or rejected. Gradual deployment is crucial, especially when you have multiple email senders for the same domain, as each needs to be properly configured.
Monitoring and refining your DMARC policy
DMARC reporting is an invaluable feature that provides insights into your email ecosystem. Aggregate reports (RUA) offer a high-level overview of email traffic, showing which emails are passing or failing DMARC authentication and from where they are originating. Forensic reports (RUF), though less commonly used due to privacy concerns, provide more detailed information about individual failed messages, which can be useful for identifying specific spoofing attempts.
These reports are crucial for understanding your email sending landscape. They help you identify legitimate senders that might not be properly authenticating, allowing you to fix any misconfigurations before enforcing a stricter DMARC policy. They also alert you to unauthorized entities attempting to send emails from your domain, giving you visibility into spoofing activities. Effective DMARC record setup and reporting are foundational to this process. For more details on how to configure your DMARC record, refer to the official Microsoft documentation.
Regularly reviewing your DMARC reports is not a one-time task, especially if you add new email sending services or change existing configurations. This ongoing monitoring ensures that your DMARC policy remains effective and that all your legitimate emails are properly authenticated. Understanding these reports is key to moving from a monitoring policy to an enforcement policy like quarantine or reject.
Monitoring policy (p=none)
Initial phase: Allows all emails to be delivered, regardless of authentication status.
Visibility: Provides comprehensive reports on all email traffic claiming to be from your domain.
Risk mitigation: No impact on legitimate email delivery, minimizing the risk of accidental blocking.
Transition policy (p=quarantine)
Gradual enforcement: Unauthenticated emails are sent to the spam folder.
User experience: Recipients might still see spam, but it's diverted from the primary inbox.
Feedback loop: Still provides reports for ongoing analysis and refinement.
Enforcement policy (p=reject)
Maximum protection: Unauthenticated emails are rejected entirely.
Domain reputation: Significantly reduces the chances of your domain being used for malicious purposes.
Deliverability: Enhances trust with mailbox providers, improving deliverability for legitimate emails.
Comprehensive domain protection
While DMARC is incredibly effective at preventing direct domain spoofing, it's not a standalone solution for all email security challenges. Spammers and phishers are constantly evolving their tactics. Therefore, DMARC should be part of a broader email security strategy that includes other best practices for email authentication and compliance, such as those recommended by Cloudflare in their DMARC guide.
Maintaining a strong domain reputation is also critical. Being listed on an email blocklist (or blacklist) can severely impact your deliverability, even if you have DMARC in place. DMARC helps protect your reputation by preventing abuse, but consistent good sending practices, proper list hygiene, and avoiding spam traps are equally important. Regularly check your domain's reputation and ensure you're not inadvertently contributing to negative signals.
In addition, consider implementing other authentication standards like BIMI (Brand Indicators for Message Identification) to visually verify your brand's identity in the inbox, further building recipient trust. While DMARC focuses on preventing unauthorized use, a comprehensive approach to email security involves layers of protection. This holistic strategy helps ensure your legitimate emails reach their intended recipients, while preventing bad actors from tarnishing your domain's reputation.
Views from the trenches
Best practices
Always begin your DMARC implementation with a policy of p=none to monitor traffic and identify all legitimate sending sources without impacting deliverability.
Thoroughly analyze aggregate DMARC reports to ensure all legitimate email senders are authenticating and aligning correctly before moving to stricter policies.
Gradually transition from p=none to p=quarantine and then to p=reject, continuously monitoring reports at each stage for any issues.
Ensure SPF and DKIM are fully configured and aligned for every legitimate email sending service, including third-party providers like ESPs and CRMs.
Maintain an updated inventory of all services authorized to send email on behalf of your domain to prevent unexpected authentication failures.
Common pitfalls
Jumping directly to a p=reject policy without proper monitoring, which can inadvertently cause legitimate emails to be blocked.
Overlooking or misconfiguring SPF or DKIM records for all legitimate sending sources, leading to DMARC failures for valid emails.
Failing to regularly review DMARC reports, missing critical insights into spoofing attempts or authentication issues.
Assuming DMARC is a complete solution for all email security threats, neglecting other important aspects like domain reputation and spam prevention.
Not accounting for email forwarding services, which can break SPF alignment and cause legitimate emails to fail DMARC checks.
Expert tips
Utilize a DMARC reporting tool to simplify the complex XML data into an understandable format, making it easier to identify legitimate and fraudulent email sources.
Understand that DMARC primarily prevents the receipt of spoofed emails, rather than stopping the attempts to send them.
Consider DMARC's impact on inbound email processing for your own domain, especially for services that might not fully honor DMARC policies.
For parked domains that never send email, immediately set a DMARC p=reject policy to definitively prevent any spoofing attempts from those domains.
Implement DMARC alongside other email security best practices, such as maintaining good list hygiene and avoiding spam traps, for a layered defense.
Marketer view
Marketer from Email Geeks says that DMARC, particularly with a 'reject' policy, is advisable for preventing spammers from sending emails that appear to originate from a domain, but it's essential to ensure all legitimate sources are aligned and passing authentication beforehand to avoid issues.
2024-01-12 - Email Geeks
Marketer view
Marketer from Email Geeks says that simply listing authorized IPs in SPF records is only a small part of DMARC's requirements, as proper alignment of the return-path with the friendly From header and DKIM signing are also crucial for every legitimate sending source.
2024-01-12 - Email Geeks
Securing your email ecosystem
Implementing DMARC with an enforced policy (like p=reject) is one of the most effective measures you can take to prevent spammers and phishers from using your domain. It empowers you to tell the world's email receivers how to handle unauthenticated mail originating from your brand, significantly reducing the success rate of spoofing attacks.
While the setup requires careful planning and ongoing monitoring of DMARC reports, the benefits in terms of enhanced brand reputation, improved email deliverability, and protection against cyber threats are substantial. By taking a proactive stance with DMARC, you not only protect your own domain but also contribute to a safer email ecosystem for everyone.
