Is strict DMARC alignment always necessary for email security?
Matthew Whittaker
Co-founder & CTO, Suped
Published 15 Nov 2025
Updated 15 Nov 2025
8 min read
The debate around DMARC alignment, specifically whether to pursue strict or relaxed modes for SPF and DKIM, is a common one among email administrators. On one hand, the idea of strict alignment offers maximum security, ensuring that every authenticated email precisely matches the sending domain. On the other, the complexities of modern email infrastructure, involving various third-party senders and subdomains, often make strict alignment a challenging, if not impossible, goal.
Many IT security teams understandably prioritize the strongest possible defenses against spoofing and phishing. Their concern often stems from past experiences with malicious actors impersonating their brand. This can lead to a firm stance on requiring strict DMARC alignment for all email streams, viewing anything less as a significant security vulnerability.
However, the reality of email deliverability for many organizations involves a complex web of services, each with its own sending methods. Balancing stringent security requirements with the practicalities of ensuring legitimate emails reach their destination requires a nuanced understanding of DMARC and its alignment modes. It's not always a straightforward choice between strict and relaxed, but rather a strategic decision based on your specific email ecosystem and risk profile.
Understanding DMARC alignment
DMARC works by checking if the domain in the From header (RFC5322.From) aligns with the domain that authenticated with SPF (RFC5321.MailFrom) or DKIM (d= domain). This concept of identifier alignment is critical for DMARC to function. You can learn more about this in our guide on how to concisely explain DMARC passing.
There are two modes for this alignment: strict and relaxed. Strict alignment requires an exact match between the organizational domains in the relevant headers. For example, if the From header is user@example.com, the SPF MailFrom domain (e.g., bounces.example.com) or DKIM d=domain must also be example.com (or a subdomain of example.com) with SPF and DKIM in strict mode respectively. Relaxed alignment is more forgiving, allowing the authenticated domains to be subdomains of the From header domain. For instance, marketing.example.com would align with example.com.
This distinction is crucial, as relaxed alignment is often necessary when using third-party email service providers (ESPs) that send emails on behalf of your domain using their own subdomains or bounce domains. A detailed explanation can be found in our article: What DMARC alignment mode is stricter, relaxed or strict?
Strict alignment (or "s" tag in SPF, or "s" tag in DKIM) requires an exact match between the organizational domain in the From header and the authenticated domain. For example, if the From header is user@example.com, the SPF MailFrom domain (e.g., bounces.example.com) or DKIM d=domain must also be example.com for strict SPF alignment.
Relaxed alignment (or "r" tag in SPF, or "r" tag in DKIM) allows the authenticated domain to be a subdomain of the From header domain. Using the same example, marketing.example.com would successfully align with example.com for relaxed SPF alignment.
The perceived security benefits of strict alignment
From a security standpoint, strict alignment offers the highest level of protection against direct domain spoofing. If an attacker tries to send an email impersonating your domain, but they can't achieve an exact match with the SPF MailFrom or DKIM d=domain, the email will fail DMARC. This gives the receiving mail server a clear signal to quarantine or reject the message, depending on your DMARC policy. This approach is highly effective in preventing unauthorized use of your primary sending domain.
The concern often voiced by IT administrators, especially those who have experienced spoofing campaigns, is that relaxed alignment might open doors for subtle forms of impersonation. For instance, if an attacker gains control of a legitimate subdomain, even if SPF or DKIM alignment is relaxed, they could theoretically send emails that pass DMARC checks. However, this scenario typically implies a compromise at a deeper level (e.g., DNS control of a subdomain), which strict DMARC alignment alone wouldn't fully mitigate, as the attacker could then configure strict alignment for their rogue subdomain.
Many major email providers, including Google, do recommend considering strict alignment for increased protection, particularly when mail is sent directly for your domain. This recommendation underscores the enhanced security strict alignment offers for controlling direct domain use. For understanding common DMARC failures, our guide on why your emails are getting a DMARC verification failed error provides further insights into how alignment impacts DMARC results.
Practical implications and challenges
The primary hurdle with strict alignment arises from the nature of modern email sending. Most organizations rely on multiple third-party services for various email functions: marketing campaigns, transactional emails, customer support, and more. These services often send emails using their own bounce domains or DKIM signing domains that are subdomains of your primary domain, making strict alignment difficult to achieve without significant configuration or, in some cases, impossible.
If a sender uses a unique subdomain for their MailFrom (envelope-from) domain, strict SPF alignment becomes impossible if that subdomain isn't explicitly delegated and configured. Similarly, many ESPs will sign emails with a DKIM domain that is a subdomain of your main domain, which would fail strict DKIM alignment. This is a common operational reality that often necessitates the use of relaxed SPF and DKIM alignment to ensure legitimate emails are delivered. We also cover DKIM alignment for Google and Yahoo in a dedicated article.
The DMARC standard (and its proposed update, DMARCbis) acknowledges these complexities. The DMARCbis draft notes that while strict alignment could theoretically prevent certain relaxed pass risks related to subdomain DNS compromise, if an attacker truly controls a subdomain's DNS, they can often achieve strict alignment for that subdomain anyway, rendering the organizational domain's strict policy less effective. You can review the DMARCbis draft for more information.
Suped provides AI-powered recommendations to help you navigate DMARC alignment complexities. Our platform doesn't just show you data; it tells you what to do with it, providing actionable recommendations to fix issues and strengthen your policy. This is invaluable when managing different sending services and their impact on your DMARC alignment.
When strict alignment makes sense
While strict alignment isn't always feasible or strictly necessary for every email stream, there are scenarios where it is highly beneficial. For core corporate communications, executive emails, or domains with extremely sensitive data, strict alignment can provide an additional layer of assurance. It signals to receiving mail servers that only emails originating from precisely aligned sources are truly authorized.
Organizations with the resources and technical capability to meticulously configure all sending systems for strict alignment should consider it for their most critical domains. This often involves careful planning with third-party vendors to ensure they can support the necessary exact domain matching for SPF and DKIM. You can explore how to safely transition your DMARC policy to quarantine or reject in our guide.
For the majority, a pragmatic approach is often best. Start with a relaxed alignment and use DMARC monitoring to gain visibility into your email ecosystem. Identify which senders are struggling with alignment and assess the risks associated with them. Suped's unified platform, offering DMARC, SPF, and DKIM monitoring alongside blocklist and deliverability insights, is an excellent tool for this. Its real-time alerts and MSP and Multi-Tenancy Dashboard make it ideal for comprehensive email security management, even for larger enterprises and service providers.
Views from the trenches
Best practices
Always start DMARC implementation with a 'p=none' policy to gather reports and understand your email traffic without impacting delivery.
Prioritize securing your core sending domains with the strongest possible DMARC policies before attempting strict alignment across all subdomains.
Regularly review DMARC reports to identify legitimate sending sources and misconfigurations that might affect alignment.
When working with third-party senders, ensure they support DMARC and can provide the necessary SPF or DKIM alignment for your domain.
Common pitfalls
Mistakenly believing DMARC alignment can prevent all forms of spoofing, especially cousin domain spoofing or look-alike attacks.
Implementing a 'p=reject' policy with strict alignment too quickly, leading to legitimate emails being blocked or quarantined.
Overlooking the complexities of third-party senders, which often require relaxed alignment for DMARC to pass.
Failing to delegate unique subdomains correctly to third-party services for SPF, preventing full alignment.
Expert tips
Use SPF flattening to avoid the 10-lookup DNS limit, which is a common issue for domains with many SPF authorized senders.
Implement DMARC at 'p=none' first and monitor your reports with a reliable tool to prevent deliverability issues.
Regularly monitor your domain's reputation using tools like Google Postmaster Tools for any signs of abuse or blocklisting.
Educate your IT and marketing teams about DMARC, SPF, and DKIM to foster a shared understanding of email security practices.
Marketer view
Marketer from Email Geeks says they often encounter IT admins who are overly concerned about strict DKIM/SPF alignment as a major security risk, even when relaxed alignment is practical.
1741891776 - Email Geeks
Marketer view
Marketer from Email Geeks says they create unique subdomains on the envelope-from domain, which makes full alignment impossible with their current setup.
1741891814 - Email Geeks
Finding the right balance for your domain
Ultimately, whether strict DMARC alignment is always necessary for email security depends on your organization's specific needs, risk tolerance, and email sending infrastructure. For some, the enhanced security of strict alignment for critical domains is paramount. For others, particularly those with diverse sending services, relaxed alignment offers a practical and secure compromise that maintains deliverability without compromising core protection.
The key is to implement DMARC with careful planning, starting with a monitoring policy (p=none) to observe your email traffic and identify any authentication issues. This allows you to gradually tighten your policy (to quarantine or reject) as you gain confidence in your DMARC compliance. It is important to ensure both SPF and DKIM are correctly configured for your sending domains.
Regardless of your chosen alignment mode, continuous DMARC monitoring is essential. Tools like Suped provide the necessary visibility and actionable insights to manage your email authentication effectively, helping you maintain strong email security and deliverability. We offer the most generous DMARC monitoring free plan on the market, so you can always stay informed about your domain's security posture.
