Do subdomains need their own DMARC records if the main domain has one?
Michael Ko
Co-founder & CEO, Suped
Published 6 Jun 2025
Updated 19 Aug 2025
7 min read
One of the most frequent questions I encounter about DMARC, especially for those managing complex email infrastructures, revolves around subdomains. The core question is whether each subdomain requires its own DMARC record if the main organizational domain already has one. It's a valid concern, as misconfigurations can severely impact email deliverability and expose your domain to spoofing.
The answer, like much in email authentication, isn't a simple yes or no. While a DMARC policy on your main domain can indeed cover subdomains by default, there are specific scenarios where adding explicit DMARC records for your subdomains is not only beneficial but essential. Ignoring this can lead to emails landing in spam folders or being rejected outright, even if your main domain's DMARC is perfectly set up.
I’ve seen firsthand how an improperly configured subdomain's DMARC, or lack thereof, can lead to deliverability issues, especially with major mailbox providers like Microsoft. These providers are increasingly stringent about email authentication. Let's delve into the mechanics of DMARC inheritance and when you need to consider dedicated subdomain policies.
By default, DMARC policies are inherited. If you publish a DMARC record for your organizational domain, say yourdomain.com, this policy will automatically apply to all its subdomains, such as marketing.yourdomain.com or newsletter.yourdomain.com. This simplifies management for many organizations, as you don't need to create individual DMARC records for every subdomain.
The DMARC record specifies how receiving mail servers should handle emails that fail DMARC authentication checks. It includes tags like p (policy), rua (aggregate report URI), and ruf (forensic report URI). The sp (subdomain policy) tag is particularly relevant here, as it allows you to define a specific DMARC policy for all subdomains, overriding the main domain's p tag for them. For more details on how this tag works, see our guide on how the DMARC sp tag affects policies.
This default inheritance is a cornerstone of DMARC's efficiency, ensuring broad protection without excessive DNS entries. However, this convenience assumes all your subdomains have the same authentication and reporting needs. When these needs diverge, that's when you must consider dedicated records.
When explicit DMARC records are needed for subdomains
While DMARC inheritance is convenient, there are critical scenarios where an explicit DMARC record for a subdomain is necessary. The primary reason is to apply a different policy or reporting address for a specific subdomain than what is set for the organizational domain. For instance, you might want a p=reject policy on a sensitive transactional subdomain but keep a p=none policy on a marketing subdomain while you're still monitoring its traffic.
Publishing a DMARC record directly on a subdomain, for example, on _dmarc.sub.yourdomain.com, will override the inherited policy from the parent domain. This is how you gain granular control over your email authentication. If you're wondering if you should add an explicit record, consider the specific sending patterns and risks associated with each subdomain.
Default DMARC inheritance
Policy Application: The policy set on the main domain (e.g., p=quarantine) applies to all subdomains unless explicitly overridden.
Reporting: All DMARC reports (aggregate and forensic) for subdomains are sent to the addresses specified in the main domain's rua and ruf tags.
Management: Centralized management of DMARC settings from a single record.
When a dedicated subdomain DMARC record is needed
You would set up a distinct record at the subdomain level to apply a different policy or specify unique reporting addresses. This allows for granular control over how each subdomain’s email is handled and reported. For more about setting up these records, check out how to set up DMARC records for subdomains.
Policy Customization: Allows different DMARC policies (e.g., p=reject for transactional emails, p=none for marketing campaigns) per subdomain.
Separate Reporting: Direct DMARC reports to different mailboxes for each subdomain, facilitating more focused analysis.
Delegation: Useful when specific subdomains are managed by different departments or third-party senders.
It’s important to note that a DMARC record on a subdomain will always override the policy set by the organizational domain, including the sp tag from the main record. This gives you the flexibility to manage unique email flows without affecting your root domain's DMARC posture. If you're using various email service providers for different subdomains, explicit records are a must to maintain proper authentication and prevent deliverability issues, as each provider might require specific configurations.
Impact on deliverability and reputation
Proper DMARC implementation, including for subdomains, directly impacts your email deliverability and sender reputation. Mailbox providers, especially Google and Yahoo, are increasingly demanding strong authentication. Failing to have a DMARC record for a subdomain actively sending email, even if the parent domain has one, can lead to authentication failures. This, in turn, can cause your emails to be flagged as spam or rejected.
A subdomain that lacks a DMARC record or has one that isn't aligned with its sending practices is more susceptible to email spoofing and phishing attempts. This is because attackers can more easily impersonate your subdomain if it lacks robust authentication, leading to reputation damage for your entire domain. This is why having robust DMARC monitoring in place is critical.
Risks of unauthenticated subdomains
Low Deliverability: Emails from unauthenticated subdomains are often routed to spam or blocked entirely, impacting campaign performance and communication.
Reputation Damage: A subdomain with poor authentication can negatively affect the sender reputation of your entire organizational domain, potentially landing it on a blocklist or blacklist.
Increased Spoofing: Without a strong DMARC policy, threat actors can easily impersonate your subdomains for phishing or malicious activities, deceiving recipients.
Ensuring DMARC alignment for all sending subdomains is a critical step in maintaining a strong sender reputation and avoiding email deliverability issues. This is especially true given the recent industry-wide push towards stricter authentication requirements from mailbox providers.
Practical considerations and troubleshooting
When encountering DMARC failures on a subdomain, even if your main domain's DMARC is seemingly correct, it's a clear signal to investigate. These failures can point to a misalignment between your subdomain’s email sending practices and its DMARC policy. This is why some senders opt for individual DMARC records on subdomains, even if it adds a bit more overhead.
For instance, if you have a subdomain like sender.clientname.com that’s experiencing high complaint rates and being sent to spam, and you notice it lacks a specific DMARC TXT entry, adding one is a logical troubleshooting step. While the root cause might lie elsewhere, such as poor sending practices or a compromised sender, ensuring full authentication for all active sending domains eliminates one potential variable. This proactive approach can help isolate the real issues and improve your deliverability. If you need help generating a record, try our free DMARC record generator tool.
It’s a best practice to ensure every domain and subdomain from which you send email has a correctly configured DMARC record. This principle extends beyond DMARC to other authentication standards like SPF. For example, Microsoft Learn states that each defined domain or subdomain in DNS requires an SPF TXT record. This philosophy of explicit authentication for all sending entities generally applies across the board, even if DMARC has an inheritance mechanism. It simplifies troubleshooting and strengthens your overall email security posture.
Views from the trenches
Best practices
Always align your DMARC records with your actual email sending practices across all subdomains to ensure proper authentication.
Utilize subdomain-specific DMARC records if different subdomains have unique sending behaviors, policies, or reporting requirements.
Proactively monitor DMARC reports for all your domains, including subdomains, to identify authentication failures and potential spoofing attempts early.
Common pitfalls
Assuming DMARC inheritance always covers all subdomains adequately, especially for subdomains with distinct sending purposes.
Neglecting to monitor DMARC aggregate reports, which can reveal issues with subdomain authentication even when policies are inherited.
Not adding a dedicated DMARC record to a subdomain experiencing deliverability issues, even if the main domain has one.
Expert tips
If a subdomain is used by a third-party sender, ensure their DMARC, SPF, and DKIM settings are correctly integrated.
For non-sending subdomains, consider publishing a DMARC record with a 'p=reject' policy to prevent spoofing.
Implement DMARC at 'p=none' initially and gradually move to 'quarantine' or 'reject' after analyzing reports for all subdomains.
Expert view
Expert from Email Geeks says that if DMARC is set up correctly, but mail still goes to spam, it's usually because the domain has a poor reputation, and DMARC confirms that identity.
2023-11-13 - Email Geeks
Expert view
Expert from Email Geeks says that a DMARC record at the organizational domain can cover all subdomains, provided no subdomain requires its own unique policy or reporting addresses.
2023-11-13 - Email Geeks
Final thoughts on DMARC and subdomains
The question of whether subdomains need their own DMARC records when the main domain has one boils down to your specific email sending architecture and policy requirements. While DMARC policies are indeed inherited, explicit subdomain records provide crucial flexibility and control, especially for diverse sending purposes or when troubleshooting deliverability issues.
Always prioritize strong authentication for all your sending domains and subdomains. This means ensuring proper DMARC, SPF, and DKIM configuration across the board. Doing so will help protect your brand from spoofing, enhance your sender reputation, and ultimately improve your email deliverability, helping your messages land where they belong – in the inbox.
Microsoft. These providers are increasingly stringent about email authentication. Let's delve into the mechanics of DMARC inheritance and when you need to consider dedicated subdomain policies.
Google and 
Yahoo, are increasingly demanding strong authentication. Failing to have a DMARC record for a subdomain actively sending email, even if the parent domain has one, can lead to authentication failures. This, in turn, can cause your emails to be flagged as spam or rejected.
