Does DMARC 'relaxed' alignment match a subdomain to the organizational domain?
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Feb 2025
Updated 29 Oct 2025
6 min read
When setting up DMARC, a crucial aspect is understanding domain alignment, particularly the difference between strict and relaxed modes. This distinction significantly affects how DMARC evaluates your emails and whether they pass authentication checks, especially when dealing with subdomains. Many wonder if the DMARC 'relaxed' alignment mode extends its matching criteria to include subdomains within the same organizational domain, and the answer is yes, it does.
Relaxed alignment is designed to provide greater flexibility. It allows email authentication protocols like SPF and DKIM to pass DMARC even if the domains don't perfectly match, as long as they belong to the same organizational domain. This is incredibly useful for organizations that use various subdomains for different departments or marketing campaigns, ensuring their legitimate emails are not mistakenly blocked.
Understanding how this mechanism works is key to successful email deliverability and robust email security. Improper configuration, or a misunderstanding of alignment, can lead to legitimate emails failing DMARC and potentially being rejected or sent to spam, affecting your communication and brand reputation. Let's delve into the specifics of relaxed alignment and its impact on subdomains.
Understanding DMARC alignment modes
DMARC leverages two underlying email authentication protocols: Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM). For a DMARC check to pass, either SPF or DKIM, or both, must align with the From header domain of the email. There are two primary alignment modes: strict (s) and relaxed (r).
In strict alignment, the domain in the SPF Return-Path header (also known as the MAIL FROM domain or Envelope From) or the DKIM d= domain must exactly match the organizational domain in the email's From header. No subdomains are allowed for a match. This is the most stringent setting and offers the highest level of protection, but it can also be the most challenging to implement correctly, especially with complex sending infrastructures.
Conversely, relaxed alignment permits the domains to be subdomains of the From header domain. As explained in detail on this external resource, if the DMARC record specifies relaxed alignment for SPF (aspf=r) or DKIM (adkim=r), it means that the domains only need to share the same organizational domain, but can have different subdomains. For a deeper understanding of this, see our article on how relaxed domain alignment works.
Strict alignment
Exact match required: The SPF MAIL FROM domain or DKIM d= domain must be identical to the From header domain.
No subdomains allowed: Even if a subdomain of the From header domain, it will fail strict alignment.
Highest security: Offers maximum protection against spoofing but requires precise configuration.
Relaxed alignment
Organizational domain match: The SPF MAIL FROM domain or DKIM d= domain only needs to share the same organizational domain as the From header domain.
Subdomains pass: This means a subdomain (e.g., mail.example.com) can align with its organizational domain (example.com).
Increased flexibility: Easier to implement for complex setups with multiple sending services.
Choosing between strict and relaxed alignment depends on your specific sending practices and security requirements. While strict alignment offers stronger protection, relaxed alignment often proves more practical for many organizations, especially those utilizing numerous subdomains or third-party sending services.
How relaxed alignment applies to subdomains
The core question is whether 'relaxed' alignment matches a subdomain to the organizational domain. In short, yes, it does. For example, if your organizational domain is example.com, and you send an email where the From header is marketing@example.com, but the SPF MAIL FROM domain is bounce.marketing.example.com, SPF would pass DMARC alignment under a relaxed policy because bounce.marketing.example.com is a subdomain of example.com.
The same principle applies to DKIM. If your From header is news@example.com, and the DKIM signature's d= domain is sendgrid.net, with a Header From domain of example.com, DKIM alignment fails without CNAME records. However, with CNAME records and relaxed alignment, if SendGrid uses a subdomain like s1._domainkey.news.example.com for its DKIM signature, which ultimately resolves to sendgrid.net, it can pass DMARC if the d= domain in the DKIM signature is news.example.com. The critical detail is that the news.example.com (DKIM d= domain) aligns with example.com (From header domain) under relaxed alignment rules. This behavior is crucial for integrating with many third-party email service providers, as highlighted by Amazon SES documentation.
This flexible matching is why relaxed alignment is often the default or recommended setting, especially when organizations use various subdomains to manage their email ecosystem. It prevents legitimate emails from being flagged as unauthenticated simply because they originate from a subdomain rather than the exact root domain.
The implications for your DMARC policy
The choice of DMARC alignment mode directly impacts your email deliverability and security posture. Using relaxed alignment for your organizational domain allows emails sent from its subdomains to pass DMARC checks, which is essential for many modern email infrastructures. If you have DMARC policies configured, relaxed alignment is typically the more practical choice, especially if you outsource email sending to third-party providers. Many ESPs send emails on behalf of your domain from their own subdomains, making relaxed alignment necessary for proper DMARC compliance.
However, this flexibility comes with a slightly reduced security posture compared to strict alignment. While it helps legitimate emails pass, a relaxed policy could theoretically be exploited by sophisticated spoofers who manage to send emails from a subdomain that isn't explicitly authorized but still aligns organizationally. This is where comprehensive DMARC monitoring becomes critical.
Best practices for DMARC and subdomains
Start with relaxed alignment: This is often the safest starting point to avoid blocking legitimate emails, especially for organizations with diverse sending patterns.
Monitor DMARC reports: Regularly analyze your DMARC reports (RUA and RUF) to identify any unauthorized sending sources or authentication failures. Tools like Suped provide AI-powered recommendations to simplify this process.
Leverage AI-powered insights: Use platforms like Suped to get actionable recommendations to strengthen your DMARC policy and enhance deliverability.
The continuous analysis of DMARC data, especially through a platform with AI-powered recommendations, allows you to refine your DMARC policy over time. This way, you can gradually move towards stricter enforcement (like p=quarantine or p=reject) while maintaining excellent deliverability.
Key takeaways
DMARC relaxed alignment is a practical and widely adopted approach to email authentication that indeed matches a subdomain to its organizational domain. This flexibility is vital for organizations utilizing complex email sending architectures, including numerous subdomains and third-party email service providers.
While providing necessary flexibility, remember that continuous monitoring and analysis of DMARC reports are essential to maintain strong email security and deliverability. By understanding how relaxed alignment works, you can ensure your legitimate emails reach their intended recipients while still benefiting from DMARC's protection against spoofing and phishing attacks.
