DMARC Policies for Organizational Domains and Subdomains Explained
Michael Ko
Co-founder & CEO, Suped
Published 11 Jun 2025
Updated 19 Aug 2025
9 min read
Understanding how DMARC policies apply across your entire domain infrastructure, including organizational domains and subdomains, is critical for comprehensive email security and deliverability. Misconfigurations can leave parts of your email ecosystem vulnerable to spoofing, phishing, and other abuses, leading to blocklists (or blacklists) and significant reputation damage.
The hierarchy of DMARC enforcement ensures that even if you don't explicitly set a policy for every subdomain, a default rule often applies. However, relying solely on inheritance can lead to unexpected behaviors or expose certain sending channels. For robust protection, you need a clear strategy for both your main domain and all associated subdomains.
In this explanation, I'll walk you through how DMARC records interact with organizational domains and subdomains, the role of the sp tag, and how to implement policies that provide maximum protection without disrupting legitimate email flows.
An organizational domain is typically the root domain of your online presence, such as yourcompany.com. A DMARC record published at this level, for example, _dmarc.yourcompany.com, establishes the baseline policy for your entire domain. By default, this policy cascades to all subdomains beneath it, unless a specific subdomain has its own DMARC record. This cascading behavior is a fundamental aspect of DMARC, designed to provide broad protection with minimal configuration. You can find more details on how DMARC works with subdomains on the DMARC.org overview page.
The main advantage of this inheritance model is that it ensures all your subdomains, including those you might not even be actively using or are unaware of, are covered by a DMARC policy. This prevents unauthorized parties from using obscure or non-existent subdomains to send phishing or spoofing emails that could harm your brand's reputation and lead to you being on a blocklist or blacklist. Without this default inheritance, managing DMARC for every single subdomain, especially in large organizations with numerous applications and services, would be an impossible task.
However, while convenient, the default inheritance can also be a double-edged sword. If your organizational domain's policy is set to p=reject or p=quarantine and a subdomain sends legitimate emails that fail DMARC authentication, those emails could be rejected or sent to spam folders. This highlights the importance of carefully planning your DMARC deployment and understanding how policies and RUA/RUF settings inherit.
Subdomain specific DMARC policies
While an organizational domain's DMARC policy applies to subdomains by default, you have the flexibility to define specific policies for individual subdomains. This is achieved by publishing a separate DMARC record directly on the subdomain (e.g., _dmarc.marketing.yourcompany.com). When a subdomain has its own DMARC record, this record overrides the policy inherited from the organizational domain. This is incredibly useful for tailoring policies to the specific needs and risk profiles of different sending channels.
For example, you might use marketing.yourcompany.com for bulk email campaigns and transactional.yourcompany.com for critical system notifications. It's common to set a more lenient policy (like p=none) for marketing subdomains initially to gather data, while implementing a stricter p=reject for transactional subdomains that are well-controlled and critical for security. This granular control is essential for preventing email spoofing and maintaining good email deliverability. If you want to dive deeper into this topic, you can read more about DMARC's RFC 7489 documentation.
There are several reasons why you might want to add an explicit DMARC record for subdomains. One common scenario is when different departments or third-party email service providers (ESPs) are responsible for sending emails from specific subdomains. By giving them their own DMARC record, you can delegate control and reporting without affecting the policy of your main domain or other subdomains. This approach allows for isolated management and troubleshooting, making it easier to identify and resolve DMARC verification failed errors.
The DMARC sp tag
The sp tag, short for subdomain policy, is a crucial DMARC tag that allows you to specify a DMARC policy for all subdomains from the organizational domain's DMARC record itself. This means you don't have to create a separate DMARC record for every subdomain if you want them all to have the same policy. Instead, you can define a policy for the main domain with p= and then a policy for all subdomains with sp=. This provides a powerful way to manage your DMARC deployment efficiently, especially for domains with many subdomains, and impacts how the DMARC sp tag affects subdomain policies.
In the example above, the organizational domain (yourdomain.com) would have a policy of quarantine, while all subdomains would have a policy of none. This is a common strategy during DMARC rollout, allowing you to enforce a policy on your main domain while gathering data and monitoring subdomains without impacting their deliverability. It's a key part of implementing simple DMARC examples starting with p=none.
However, it's important to note that the sp tag in an organizational domain's DMARC record will be ignored if a specific subdomain has its own DMARC record. The subdomain's explicit record will always take precedence. This hierarchical structure allows for both broad default coverage and fine-grained control where needed, enabling you to override root domain DMARC policies.
Best practices for DMARC deployment
Implementing DMARC effectively across your organizational domain and subdomains requires a thoughtful approach. Here's how to ensure comprehensive protection and smooth email delivery:
Start with p=none: Begin with a p=none policy on your organizational domain, especially if you have many subdomains or unknown sending sources. This allows you to gather DMARC reports without impacting legitimate email. This is crucial for understanding and troubleshooting DMARC reports from Google and Yahoo.
Leverage sp: Use the sp tag on your organizational domain to set a general policy for subdomains. This is particularly useful if you want to keep subdomains at p=none while moving your main domain to p=quarantine or p=reject.
Specific subdomain policies: For critical or high-volume sending subdomains, consider publishing dedicated DMARC records to apply stricter policies or to manage them independently. This allows for granular control over best practices for DMARC setup.
As you move towards stricter policies, ensure that all legitimate sending sources are properly authenticated with SPF and DKIM. Any email failing authentication under a p=quarantine or p=reject policy will be impacted. The goal is to reach a state where you can confidently enforce p=reject on all your domains and subdomains, preventing all unauthorized use. You can refer to our guide on safely transitioning your DMARC policy to higher enforcement levels.
Monitoring your DMARC reports is essential throughout this process. These reports provide invaluable insight into email authentication failures and legitimate sources that might not yet be configured correctly. Use this data to identify and rectify issues before moving to a more restrictive policy. Comprehensive DMARC monitoring tools can help automate this process.
Practical policy application
Scenario 1: Organizational policy only
Configuration: A single DMARC record on yourdomain.com with p=reject and no sp tag.
Effect: All subdomains (e.g., marketing.yourdomain.com, sales.yourdomain.com) will inherit p=reject. This is simple but high-risk if subdomains aren't fully compliant.
Scenario 2: Organizational policy with sp tag
Configuration: A DMARC record on yourdomain.com with p=reject and sp=none.
Effect:yourdomain.com is protected by reject, but subdomains are monitored with none. This is safer during initial rollout.
Consider the following table to understand the DMARC tag behaviors:
DMARC Tag
Description
Impact on policies
p
The policy for the organizational domain. Can be none, quarantine, or reject.
Applies to the organizational domain and its subdomains by default, if no sp or specific subdomain DMARC record exists.
sp
The policy for all subdomains when defined on the organizational domain's DMARC record. Can be none, quarantine, or reject.
Overrides the p tag for subdomains only. An explicit DMARC record on a subdomain will override sp.
Using both the p and sp tags provides the most flexible way to manage your DMARC deployment, offering both broad coverage and specific policy tailoring. This ensures that all your email streams are properly protected and align with your overall security posture.
Key takeaways
Important considerations for DMARC policies
While DMARC provides powerful protection, careful planning is essential. A common pitfall is moving to a reject policy too quickly without thoroughly analyzing DMARC reports. This can lead to legitimate emails being blocked, impacting business operations and potentially causing your sending domains to land on a blocklist (or blacklist).
Remember that DMARC builds upon SPF and DKIM. Ensure these underlying authentication mechanisms are correctly configured for all your sending sources, including third-party senders, for both your organizational domain and all subdomains. Regular review of your SPF and DKIM records is key to maintaining DMARC compliance and preventing deliverability issues.
Views from the trenches
Best practices
Always start with a `p=none` DMARC policy to collect reports and identify all legitimate email sending sources before enforcing stricter policies.
Use the `sp` tag on your organizational domain to apply a consistent DMARC policy to all subdomains, simplifying management.
Publish explicit DMARC records on subdomains for granular control over specific sending channels, especially for critical or third-party services.
Regularly monitor DMARC aggregate and forensic reports to identify authentication failures and ensure legitimate emails are not being blocked.
Ensure that SPF and DKIM are correctly configured and aligned for all email sending sources across both your main domain and subdomains.
Common pitfalls
Jumping directly to a `p=quarantine` or `p=reject` policy without adequate monitoring, potentially blocking legitimate emails.
Overlooking or forgetting about subdomains, which can inadvertently inherit a strict DMARC policy and lead to deliverability issues.
Not maintaining accurate SPF and DKIM records, causing DMARC alignment failures even for authorized email senders.
Failing to review DMARC reports regularly, missing critical insights into email authentication problems and potential abuse.
Assuming DMARC coverage for all subdomains without verifying inheritance or specific subdomain policies, leaving gaps in protection.
Expert tips
Prioritize securing your organizational domain first, then extend protection to subdomains using a phased approach.
Implement stricter policies on subdomains used for sensitive communications (e.g., transactional emails) once full compliance is achieved.
Educate your team on DMARC policies to prevent unintended changes or misconfigurations that could affect email deliverability.
Consider using a DMARC management platform for easier monitoring, reporting, and policy adjustments across complex domain structures.
When dealing with reputation issues, especially with providers like Google, a 'low and slow' approach to sending volume can be highly effective.
Marketer view
A marketer from Email Geeks says that if you set DMARC for the main domain, it applies to all mail sent from that domain, plus any subdomains that don’t have their own records. If you set it at the subdomain, then it will only apply to that specific subdomain.
May 16, 2019 - Email Geeks
Expert view
An expert from Email Geeks says that you can use the sp= tag in the DMARC record at the organizational domain to have different policies for it and its subdomains, which is often very useful for managing email flow.
May 16, 2019 - Email Geeks
Conclusion
Managing DMARC policies for both organizational domains and subdomains is fundamental to building a robust email security posture. By understanding the inheritance model, the utility of the sp tag, and the importance of specific subdomain records, you can implement a DMARC strategy that protects your brand from impersonation and ensures your legitimate emails reach their intended recipients without hitting a blocklist or blacklist. Continuous monitoring and a phased approach to policy enforcement are key to a successful DMARC journey.
SPF and DKIM. Ensure these underlying authentication mechanisms are correctly configured for all your sending sources, including third-party senders, for both your organizational domain and all subdomains. Regular review of your SPF and DKIM records is key to maintaining DMARC compliance and preventing deliverability issues.
