What DMARC alignment mode is stricter: 'relaxed' or 'strict'?
Matthew Whittaker
Co-founder & CTO, Suped
Published 5 Mar 2025
Updated 19 Oct 2025
7 min read
When you configure DMARC for your domain, one of the crucial decisions you make involves setting the alignment modes for SPF and DKIM. These modes, 'relaxed' or 'strict', dictate how closely the domain in your email headers must match the domains authenticated by SPF and DKIM. Understanding this difference is fundamental to both your email security posture and ensuring your legitimate emails reach their intended recipients.
The choice between these two modes directly affects how DMARC evaluates incoming emails, influencing how strictly your email is authenticated. A stricter alignment offers greater protection against impersonation and phishing, but it also carries a higher risk of legitimate emails failing authentication if not properly configured. Conversely, a relaxed approach provides more flexibility, which can be beneficial in complex sending environments, though it reduces the overall security.
Understanding DMARC alignment modes
DMARC works by checking two key authentication protocols, SPF and DKIM, and then verifying if the domains used in these protocols align with the domain in the From header of your email. This process is known as identifier alignment. The DMARC record specifies how SPF and DKIM alignment should be handled using the aspf tag for SPF and the adkim tag for DKIM, each of which can be set to either r for relaxed or s for strict. You can find out more about these tags in our list of DMARC tags and their meanings.
The RFC5322.From header domain, also known as the organizational domain, is the one visible to recipients in their email client. For an email to pass DMARC, at least one of SPF or DKIM must pass authentication, AND its authenticated domain must align with the RFC5322.From domain based on the configured alignment mode. This is where the strictness comes into play, as the alignment requirements can vary significantly.
The RFC 7489, which defines DMARC, clearly outlines these alignment types. Understanding these modes is crucial for preventing spoofing attacks and ensuring proper email deliverability. Choosing the right mode helps you balance security and operational flexibility for your sending infrastructure.
Relaxed alignment
Relaxed alignment, specified as aspf=r for SPF and adkim=r for DKIM, is the less stringent option. For SPF, relaxed alignment means that the domain in the RFC5322.From header (the visible sender domain) only needs to share the same organizational domain as the RFC5321.MailFrom domain (the envelope sender) for the SPF check to pass alignment. This allows for subdomains to pass alignment, such as when example.com is the From header domain and m.example.com is the MailFrom domain. This functionality is detailed further in our guide How does relaxed domain alignment work in DMARC and SPF. Similarly, for DKIM, relaxed alignment allows the d= domain in the DKIM signature to be a subdomain of the RFC5322.From header domain. For instance, if your From header is example.com and the DKIM d= domain is marketing.example.com, it would still pass alignment in relaxed mode. More insights can be found in our article: Does DMARC relaxed alignment match a subdomain to the organizational domain.
When to consider relaxed alignment
Relaxed alignment is often suitable for organizations that rely on third-party sending services (such as ESPs, CRM platforms, or marketing automation tools) that send emails on behalf of their domain. These services frequently use subdomains or different MailFrom or DKIM d= domains to handle your email traffic. Relaxed alignment prevents legitimate emails from failing DMARC in these scenarios, preserving your email deliverability, though it does offer less granular protection than strict mode.
While offering flexibility, relaxed alignment does inherently provide a less stringent level of protection against direct domain spoofing. An attacker could potentially send emails from a subdomain that still aligns in relaxed mode, making it harder for receivers to distinguish between legitimate and malicious emails originating from what appears to be your domain. This tradeoff between flexibility and security is a key consideration.
Strict alignment
Strict alignment, denoted by aspf=s for SPF and adkim=s for DKIM, is, as the name suggests, the stricter mode. In strict SPF alignment, the RFC5321.MailFrom domain must exactly match the RFC5322.From header domain. This means subdomains will not pass SPF alignment. Similarly, for DKIM, the d= domain in the DKIM signature must precisely match the RFC5322.From header domain, disallowing subdomains from aligning. This strict requirement significantly enhances security against domain impersonation. You can learn more about its impact in our article: Does SPF alignment with aspf=strict provide email deliverability benefits?
Relaxed alignment pros and cons
Flexibility: Easily accommodates third-party sending services that use subdomains.
Reduced complexity: Simpler to implement initially, especially for organizations with diverse sending architectures.
Lower security: Offers less protection against subdomain spoofing, as it still allows for some variance.
Potentially weaker brand trust: May allow slightly more room for imposters to operate if not carefully monitored.
Strict alignment pros and cons
Highest security: Provides the strongest defense against direct domain spoofing and phishing attacks.
Enhanced brand reputation: More consistent brand identity across all email communications.
Increased configuration complexity: Requires all sending sources to precisely align, which can be challenging with third parties.
Higher risk of legitimate email blocking: Improper configuration can lead to legitimate emails being blocked or marked as spam.
Implementing strict alignment means that if any legitimate email sender fails to achieve exact domain alignment, that email will fail DMARC and be subject to your DMARC policy (e.g., quarantine or reject). This requires meticulous configuration of all email sending services and careful monitoring of DMARC reports. While more challenging, strict alignment offers the highest level of trust and security for your domain. Overall, strict alignment is the stricter of the two modes, offering greater security but demanding more precise setup and maintenance.
Choosing the right alignment for your domain
The optimal DMARC alignment mode for your domain depends largely on your email sending ecosystem and your risk tolerance. Many organizations start with relaxed alignment, especially during their initial DMARC deployment phase, as it minimizes the risk of inadvertently blocking legitimate emails. This approach allows you to gather DMARC reports, identify all legitimate sending sources, and address any authentication issues without impacting deliverability.
Once you have a clear understanding of your email traffic and have successfully authenticated all your legitimate sending sources, you can gradually move towards strict alignment. This transition helps bolster your domain's security and protect your brand from advanced phishing and spoofing attacks. It's an iterative process that requires careful monitoring and adjustment.
Manage your DMARC alignment with Suped
Navigating DMARC alignment, especially when transitioning to a stricter policy, can be complex. Suped simplifies this process with a unified platform offering real-time DMARC monitoring, SPF, and DKIM insights. Our AI-powered recommendations provide actionable steps to fix issues and strengthen your alignment, helping you confidently move to strict policies. With a generous free plan and robust features for MSPs, Suped is the best DMARC reporting/monitoring tool available to help secure your email.
Effective DMARC management, including alignment decisions, is crucial for maintaining a strong email domain reputation and preventing your emails from landing in the spam folder or being blocked by blocklists. A comprehensive DMARC strategy not only protects your recipients but also safeguards your brand integrity.
Securing your email with DMARC alignment
DMARC alignment modes, 'relaxed' and 'strict', are crucial for defining your domain's email security. Strict alignment is definitively the more stringent option, requiring an exact match between authentication domains and the RFC5322.From header. While it offers superior protection against spoofing and phishing, it also demands precise configuration of all sending services to avoid legitimate emails failing authentication.
Relaxed alignment, on the other hand, provides greater flexibility, accommodating subdomains and complex sending environments with third-party providers. This makes it a popular starting point for DMARC implementation. The key is to understand your sending ecosystem, monitor your DMARC reports, and strategically transition towards stricter alignment to enhance your email security over time. With tools like Suped, managing this transition and ensuring your emails are always authenticated correctly becomes a streamlined and manageable process.
