Summary
DMARC records on subdomains override root domain DMARC policies because email receivers prioritize the most specific record. If a subdomain has its own DMARC record, it's used for authentication and reporting, overriding the parent domain's policy. This enables tailored email authentication strategies for different parts of a domain. If a subdomain lacks a DMARC record, it might inherit the root domain's policy or default to receiver handling.
Key findings
- Override: Subdomain DMARC records take precedence over root domain DMARC records when present.
- Specificity: Receiving servers prioritize the most specific DMARC record.
- Tailored Policies: Subdomains can have distinct DMARC policies for granular control.
- Organizational Control: DMARC enables different policies for various parts of an organization's domain.
Key considerations
- Record Existence: If a subdomain lacks a DMARC record, behavior depends on receiver implementation; it may inherit the root's policy.
- Policy Tailoring: Ensure DMARC policies are tailored to each subdomain's needs and security requirements.
- Hierarchical Approach: Understand the hierarchical nature of DMARC evaluation, with subdomain records being checked first.
- Authentication Strategy: Tailored email authentication strategies can be applied on a per-subdomain basis.
What email marketers say
9 marketer opinions
A DMARC record on a subdomain overrides the DMARC policy set at the root domain level. This is because email receivers prioritize the most specific DMARC record available, and a subdomain record is considered more specific than the root domain record. This allows for tailored email authentication policies for different parts of a domain, enabling more granular control and flexibility.
Key opinions
- Override: Subdomain DMARC records always take precedence over root domain records.
- Specificity: Email receivers prioritize the most specific DMARC record, leading them to choose subdomain records when present.
- Granular Control: Subdomains can have distinct DMARC policies, offering finer control over email authentication strategies.
Key considerations
- Policy Tailoring: Organizations should tailor DMARC policies on subdomains to meet specific needs and security requirements.
- Record Existence: If a subdomain lacks a DMARC record, it may inherit the root domain's policy or default to the receiver's handling, depending on the circumstances.
- Authentication Strategy: Subdomain-specific DMARC records allow for implementing diverse authentication strategies for different parts of the domain.
Marketer view
Email marketer from emailsecurityfaq.com explains that a DMARC policy on a subdomain overrides the root domain’s policy. This allows different policies for different parts of a domain, providing more granular control over email authentication.
12 May 2023 - emailsecurityfaq.com
Marketer view
Email marketer from quora.com mentions that DMARC policies are inherited by subdomains unless a specific DMARC record is defined for the subdomain. If a subdomain has its own DMARC record, it overrides the parent domain’s policy.
1 Oct 2024 - quora.com
What the experts say
3 expert opinions
DMARC policy application prioritizes the most specific record. If a subdomain has its own DMARC record, it overrides the root domain's policy, allowing for different rules for different parts of the domain. Email receivers check for a DMARC record at the 'From:' domain, and if not found, then they look at the organizational domain. Only two records are considered in this process.
Key opinions
- Override: Subdomain DMARC records override root domain policies when they exist.
- Specificity: Email receivers look for the most specific DMARC record, i.e., the subdomain record.
- Domain Hierarchy: The 'From:' domain is checked first, followed by the organizational domain if no record is found.
Key considerations
- Subdomain Rules: Implement specific DMARC rules for subdomains to tailor email authentication strategies.
- Policy Tailoring: Tailor policies for each subdomain to address their specific needs and security concerns.
- Record Existence: Ensure that subdomains have their own DMARC records if different policies are desired than the root domain.
Expert view
Expert from SpamResource explains that if a subdomain has its own DMARC record, it will override the DMARC policy of the root domain. This is because email receivers will look for the most specific DMARC record applicable to the sending domain, and a subdomain record is more specific than a root domain record.
11 Jul 2023 - SpamResource
Expert view
Expert from Email Geeks shares that if the domain in the From: header has a DMARC record that applies. If not, then the sp= (or p= if there’s no sp=) in the DMARC record at the organizational domain applies. You never look at more than two records: the one in the From: domain and the organizational domain, not anything in between.
17 Jan 2024 - Email Geeks
What the documentation says
6 technical articles
DMARC records on subdomains override the parent domain's DMARC policy for that specific subdomain because the evaluation process follows a hierarchical approach, checking for the most specific record first. If a subdomain has its own DMARC record, it's used for email authentication and reporting, and the root domain's `sp` tag doesn't apply. If a subdomain lacks a DMARC record, it may inherit the root domain's policy.
Key findings
- Override: A subdomain DMARC record takes precedence over the root domain's policy for that subdomain.
- Hierarchical Evaluation: DMARC evaluation checks for the most specific record first (subdomain), then moves up to the organizational domain.
- Subdomain Independence: If a subdomain has a DMARC record, it does not inherit or require a parent domain record.
Key considerations
- Policy Management: Using subdomain DMARC records is a common way to manage email authentication differently across an organization.
- Specific Policies: Domain owners can use subdomain DMARC records to subject subdomains to different policies.
- DMARC Mechanism: DMARC provides a mechanism for specifying policies that apply to subdomains, overriding parent domain policies.
Technical article
Documentation from support.google.com explains that DMARC policies work hierarchically. A subdomain's DMARC record will take precedence over the root domain's record for that subdomain's email traffic. If a subdomain doesn't have a DMARC record, it inherits the root domain's policy.
13 Jun 2023 - support.google.com
Technical article
Documentation from rfc-editor.org states that DMARC provides a mechanism for domain owners to indicate that subdomains should be subject to different policies, and a receiving server will use the most specific policy available, effectively overriding parent domain policies.
13 Sep 2023 - rfc-editor.org
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