What are the implications of rolling out DMARC for a sending domain?
Michael Ko
Co-founder & CEO, Suped
Published 21 May 2025
Updated 18 Aug 2025
8 min read
When you're running email campaigns or managing transactional emails, ensuring your messages reach the inbox is paramount. DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a critical email authentication protocol that helps achieve this by protecting your domain from unauthorized use and improving deliverability. Many organizations, especially those using platforms like Marketo or other third-party sending services, might already have SPF and DKIM set up, but DMARC often remains the missing piece. It’s natural to wonder about the implications of rolling out DMARC for your sending domain, and what unexpected challenges or benefits might arise.
Implementing DMARC is a strategic move that affects email security, brand reputation, and overall deliverability. It allows you to specify how receiving mail servers should handle emails that claim to be from your domain but fail SPF or DKIM authentication. While the immediate thought might be about preventing spoofing, the ripple effects on your email program are much broader. Let's explore what you should anticipate when you decide to deploy DMARC.
The initial step in rolling out DMARC involves setting your policy to p=none, also known as monitoring mode. This policy instructs receiving mail servers not to take any enforcement action on emails that fail DMARC, but instead to send you reports about them. This is a crucial phase, as it provides invaluable insights into your email ecosystem without risking the deliverability of legitimate mail. During this period, you'll receive aggregated DMARC reports (RUA records) and forensic reports (RUF records), which detail where emails purporting to be from your domain are originating from, and how they are authenticating against SPF and DKIM.
The primary benefit of starting with p=none is enhanced visibility. Before DMARC, you might have been unaware of all the sources sending emails on behalf of your domain, including legitimate third-party senders (like your marketing automation platform or CRM) and, more importantly, malicious actors attempting to spoof your brand. These reports will highlight any legitimate sending sources that are not properly authenticated or aligned with DMARC, allowing you to address these issues proactively. They will also reveal any ongoing spoofing or phishing attempts using your domain, giving you the data needed to understand the scope of the problem.
Crucially, rolling out DMARC with a p=none policy has zero impact on your email deliverability. Since no enforcement action is taken, even emails that fail DMARC will still be delivered. This makes it a safe starting point to gather the necessary intelligence before moving to stricter policies. I always recommend using a p=none policy as a first step in your DMARC journey. It's a low-risk, high-reward strategy for gaining clarity on your email sending landscape.
Once you've analyzed your DMARC reports and confirmed that all legitimate email sources are properly authenticated (SPF and DKIM pass) and aligned, the next phase involves increasing your DMARC policy to p=quarantine or p=reject. This is where DMARC truly begins to enforce your sender policy and protect your domain. A p=quarantine policy tells receiving servers to place unauthenticated emails from your domain into the recipient's spam or junk folder. A p=reject policy is the strongest, instructing servers to outright reject such emails.
The primary implication of moving to an enforcement policy is a significant boost in your domain's security and brand protection. By instructing receiving mail servers to quarantine or reject unauthenticated emails, you effectively prevent malicious actors from spoofing your domain for phishing, spam, or business email compromise (BEC) attacks. This not only safeguards your brand reputation but also protects your recipients from fraudulent communications. Recent changes by major mailbox providers like Google and Yahoo for bulk senders underscore the growing importance of DMARC enforcement for deliverability. Without DMARC, particularly for senders above the 5,000 emails per day threshold, messages are more likely to be sent to spam or blocked entirely.
However, the implications of using a stricter DMARC policy mean that if legitimate emails fail authentication and alignment, they will also be subject to your DMARC policy (quarantine or reject). This is why the monitoring phase with p=none is so vital, allowing you to identify and fix any issues before they impact deliverability. Moving to p=reject is the ultimate goal for maximum protection and deliverability, provided all your sending sources are correctly configured.
Implementing DMARC can significantly improve email deliverability over time. Mailbox providers often favor domains with strong DMARC policies, viewing them as more trustworthy. This can lead to better inbox placement, reduced spam classifications, and ultimately, higher engagement rates for your email campaigns. It's a key factor in building and maintaining a positive sender reputation. Additionally, the continuous reporting allows for ongoing monitoring and adjustments, ensuring long-term email health.
P=quarantine
Action: Emails failing DMARC authentication are moved to the recipient's spam or junk folder.
Impact: Reduces visibility of spoofed emails in inboxes, but doesn't entirely block them.
Risk: Some legitimate emails might end up in spam if authentication is not perfectly configured for all senders.
P=reject
Action: Emails failing DMARC authentication are completely rejected and not delivered.
Impact: Strongest protection against spoofing and phishing, ensuring only authenticated emails reach inboxes.
Risk: Highest risk of blocking legitimate emails if any sending source is not fully DMARC compliant.
Navigating potential DMARC challenges
While DMARC offers significant benefits, its implementation isn't without potential challenges. One common hurdle involves forwarded emails. When an email is forwarded, its SPF authentication can break because the IP address changes. While DKIM often survives forwarding, if only SPF was in alignment, this can lead to DMARC failure. This is why it's crucial to have both SPF and DKIM properly configured and aligned for all your legitimate sending sources. Without careful planning, DMARC can impact email forwarding, potentially causing legitimate forwarded emails to be quarantined or rejected.
Another challenge stems from third-party email service providers (ESPs). Many organizations use multiple ESPs for different sending purposes (e.g., marketing, transactional, customer service). Each of these services must be correctly configured to send DMARC-compliant email on your behalf. This usually involves ensuring that your SPF record includes the ESP's sending IP addresses and that their DKIM signing aligns with your domain. If an ESP isn't configured correctly, emails sent through them could fail DMARC and impact your deliverability. This is one of the key challenges for DMARC implementation
Ongoing monitoring is critical. DMARC reports (the XML files) can be complex and challenging to interpret manually. Without a dedicated tool or service to parse and visualize these reports, you might miss crucial information about authentication failures or unauthorized sending. This lack of insight can lead to legitimate emails being blocked if you move to enforcement policies too quickly, potentially causing a drop in email reputation and open rates. Ensuring proper DMARC alignment, where the domain in the From: header aligns with the SPF or DKIM authenticated domain, is paramount to avoiding these issues.
Ultimately, the gradual rollout of DMARC, starting with monitoring and carefully progressing to quarantine and then reject, is the safest and most effective approach. This phased deployment allows you to identify and resolve any authentication or alignment issues without negatively impacting your email deliverability. It's a journey, not a sprint, to achieving full DMARC enforcement and maximizing its benefits for your email program.
Key DMARC failure reasons
SPF failure: The sending IP address is not authorized in the SPF record.
DKIM failure: The email's DKIM signature is invalid or missing.
Alignment failure: The domain in the From: header doesn't match the SPF or DKIM authenticated domain.
Forwarded emails: SPF often breaks on forwarding, leading to DMARC failures if DKIM isn't correctly aligned.
Views from the trenches
Best practices
Start with a DMARC policy of p=none to gather data without impacting delivery.
Analyze DMARC reports regularly to identify all legitimate sending sources and unauthorized activity.
Ensure all third-party email senders are properly configured for SPF and DKIM alignment.
Common pitfalls
Skipping the p=none monitoring phase and directly enforcing a quarantine or reject policy.
Not configuring SPF or DKIM for all legitimate sending services before DMARC enforcement.
Ignoring DMARC reports, leading to undetected issues with email authentication or spoofing.
Expert tips
Use a DMARC monitoring tool to parse complex XML reports into an understandable format.
Periodically review your DMARC record and DNS settings for any misconfigurations or outdated entries.
Educate your team on DMARC's importance to ensure compliance across all email sending operations.
Marketer view
Marketer from Email Geeks says that starting with a p=none policy allows for data collection before planning further DMARC enforcement steps.
2023-01-15 - Email Geeks
Marketer view
Marketer from Email Geeks recommends applying DMARC to the organizational domain to gain comprehensive visibility into all email streams.
2023-03-20 - Email Geeks
Final thoughts on DMARC deployment
Rolling out DMARC for your sending domain is a strategic move that significantly enhances email security, protects your brand, and improves deliverability. While the journey involves careful planning and monitoring, especially when transitioning to enforcement policies, the benefits far outweigh the complexities. By diligently analyzing DMARC reports and ensuring proper authentication and alignment for all your sending sources, you can build a more secure and reliable email program.
The implications range from gaining unprecedented visibility into your email traffic to preventing devastating spoofing attacks and improving inbox placement. It’s an essential step in modern email management, ensuring that your messages reach their intended recipients securely and effectively.
