How does relaxed domain alignment work in DMARC and SPF?
Matthew Whittaker
Co-founder & CTO, Suped
Published 16 Apr 2025
Updated 17 Aug 2025
7 min read
Understanding how relaxed domain alignment works in DMARC and SPF is critical for effective email deliverability and security. When sending emails, multiple domains are involved, and DMARC requires that the domain visible to the recipient (the From header domain, or RFC5322.From) aligns with the domains used for authentication, specifically with SPF and DKIM. This alignment can be set to either strict or relaxed mode, with significant implications for how your emails are treated by receiving servers.
Relaxed alignment offers more flexibility, allowing for some variations between these domains while still passing DMARC checks. This is often the preferred mode for many organizations due to its balance of security and operational ease. While strict alignment demands an exact match, relaxed alignment is more forgiving, especially when dealing with subdomains or third-party sending services.
Understanding these nuances helps prevent legitimate emails from being flagged as spam or phishing attempts, ensuring they reach the inbox. It also plays a role in how Google Postmaster Tools or other diagnostic tools interpret your email authentication status.
This article explains relaxed domain alignment for SPF within the context of DMARC, providing examples and best practices to ensure your emails are both secure and deliverable.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) is built upon two underlying email authentication protocols: SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). While SPF and DKIM verify different aspects of an email's authenticity, DMARC brings them together and introduces the concept of "identifier alignment."
Identifier alignment means that the domain used in the RFC5322.From header (the sender's address visible to the recipient) must match, or be related to, the domain authenticated by SPF or DKIM. Without this alignment, even if SPF or DKIM pass their initial authentication checks, the DMARC check can still fail, leading to potential delivery issues or blacklisting (or blocklisting). This is why SPF alignment issues can be reported even when SPF itself passes.
DMARC offers two modes for alignment: strict (s) and relaxed (r). These modes are defined within your DMARC record using the aspf tag for SPF alignment and adkim for DKIM alignment. The default setting if no tag is specified is relaxed.
Relaxed SPF alignment in detail
When it comes to SPF, relaxed alignment means that the RFC5322.From header domain and the RFC5321.MailFrom (or Return-Path) domain do not need to be an exact match. Instead, they only need to share the same organizational domain. This flexibility is incredibly useful for organizations that use subdomains for different email sending purposes, like marketing emails from marketing.yourdomain.com or transactional emails from transaction.yourdomain.com.
The organizational domain is essentially the root domain, plus one level, for public suffixes. For example, for marketing.example.com, the organizational domain is example.com. This means if your From header is user@yourdomain.com and your Return-Path is bounce@mta.yourdomain.com, they would align under relaxed SPF because both share the organizational domain yourdomain.com. This is a key reason why relaxed alignment is generally recommended for most organizations.
In contrast, strict alignment (aspf=s) requires an exact domain match. So, user@yourdomain.com would only align with a Return-Path of bounce@yourdomain.com, but not with a subdomain like bounce@mta.yourdomain.com. This strictness can often lead to legitimate emails failing DMARC, especially when using email service providers that send from their own subdomains, potentially impacting email deliverability.
Implementing relaxed SPF alignment
Setting up relaxed SPF alignment in your DMARC record is straightforward. You simply add aspf=r to your DMARC TXT record. If this tag is omitted, relaxed alignment is the default behavior for SPF.
Here's an example of a DMARC record with relaxed SPF alignment:
In this example, p=none means that no action is taken on failing emails, and rua specifies where aggregate reports should be sent. The aspf=r explicitly sets SPF alignment to relaxed. You can learn more about different DMARC tags and their meanings for a comprehensive understanding.
It's important to remember that SPF authentication itself, separate from DMARC alignment, primarily checks the RFC5321.MailFrom domain against the SPF record published for that exact domain. SPF does not inherently have a concept of inheritance for subdomains in the same way DMARC does. DMARC alignment is an additional layer of verification that ensures the domains are related in a way that aligns with your brand's sending identity.
Examples of relaxed SPF alignment
Let's illustrate how relaxed SPF alignment works with a few examples. In the table below, we compare various scenarios for the RFC5322.From (header From) domain and the RFC5321.MailFrom (Return-Path) domain to determine their SPF alignment status under relaxed mode.
RFC5322.From Domain
RFC5321.MailFrom Domain (Return-Path)
Organizational Domain Match
Relaxed SPF Alignment
yourdomain.com
yourdomain.com
Yes
Aligned
yourdomain.com
mta.yourdomain.com
Yes
Aligned
sub1.yourdomain.com
sub2.yourdomain.com
Yes
Aligned
yourdomain.com
anotherdomain.com
No
Not Aligned
As you can see, as long as the base organizational domain matches, SPF will be considered aligned by DMARC in relaxed mode. This is crucial for email senders who use various subdomains or rely on third-party services that often rewrite the Return-Path to one of their own subdomains (e.g., bounces.sendgrid.net). In such cases, if SPF is the only passing authentication method, relaxed alignment allows these emails to pass DMARC.
Relaxed versus strict alignment
Strict alignment
Exact Match: The RFC5322.From domain must exactly match the RFC5321.MailFrom (Return-Path) domain.
Less Flexibility: Subdomains will fail alignment unless they are an exact match, which can cause issues with ESPs or internal systems that use subdomains.
Higher Security: Provides the strongest protection against domain spoofing due to its precise matching requirements.
While offering tighter security, strict alignment often leads to legitimate emails failing DMARC, particularly for organizations with complex sending infrastructures or those using shared IP addresses from ESPs.
Relaxed alignment
Organizational Domain Match: The RFC5322.From domain and RFC5321.MailFrom domain must share the same base organizational domain (e.g., example.com and sub.example.com are aligned).
Greater Flexibility: Accommodates various email sending setups, including those with subdomains or third-party email providers.
Sufficient Protection: While less stringent, it still provides a robust level of spoofing protection and is often sufficient for most use cases.
For most senders, relaxed alignment is the optimal choice as it balances robust security with practical operational needs, ensuring deliverability without excessive false positives. You can dive deeper into strict versus relaxed alignment for more insights.
Choosing the right alignment mode depends on your organization's email sending patterns and risk tolerance. For complex environments, or those leveraging multiple sending platforms (like different marketing, transactional, and internal email systems), relaxed alignment is often a safer and more practical choice. It minimizes the risk of legitimate emails failing DMARC checks, which can lead to emails going to spam or being outright rejected by recipient servers.
Even with relaxed alignment, it is essential to monitor your DMARC reports to identify any potential alignment failures or unauthorized sending. These reports provide valuable insights into your email ecosystem, helping you maintain good sender reputation and prevent spoofing. Regularly reviewing these reports is a core part of effective DMARC monitoring.
Final thoughts
Relaxed SPF alignment provides a balance between robust email authentication and operational flexibility, making it a suitable choice for most organizations implementing DMARC. By allowing subdomains to align with the organizational domain, it ensures that legitimate email flows, especially those from third-party services, are not incorrectly blocked.
While Google themselves state that relaxed alignment typically provides sufficient spoofing protection, maintaining awareness of your email streams and regularly reviewing DMARC reports remains essential. This proactive approach ensures your emails consistently reach their intended recipients, free from the threats of spoofing and phishing.
Views from the trenches
Best practices
Always include an 'aspf' tag in your DMARC record, even if using the default relaxed mode (aspf=r) to make your policy explicit.
Use relaxed alignment for SPF (aspf=r) when leveraging email service providers (ESPs) that send from subdomains.
Regularly review your DMARC aggregate reports to ensure SPF alignment is consistently passing for your legitimate email traffic.
Ensure your SPF records are correctly published and include all authorized sending IP addresses and domains.
Common pitfalls
Assuming SPF passing automatically means DMARC alignment is also passing, which is incorrect as alignment is a separate DMARC check.
Using strict SPF alignment (aspf=s) without a clear understanding of its implications, leading to legitimate emails failing DMARC.
Not monitoring DMARC reports, which conceals misconfigurations or unauthorized sending attempts that fail alignment.
Neglecting to publish SPF records for subdomains when DMARC alignment is set to strict, causing authentication failures.
Expert tips
Verify your DMARC record's SPF alignment setting using a DMARC record generator or checker to confirm it's correctly configured.
For complex email environments, consider a phased DMARC implementation, starting with a 'p=none' policy before moving to quarantine or reject.
If you encounter SPF alignment failures, check the Return-Path domain in your email headers and verify it shares the organizational domain with your From header.
Educate your team on DMARC alignment concepts to prevent configuration errors that could impact email deliverability.
Expert view
Expert from Email Geeks says: Any two hostnames that share an organizational domain are aligned under relaxed DMARC.
2023-07-26 - Email Geeks
Expert view
Expert from Email Geeks says: SPF by itself does not have a concept of alignment or inheritance; it simply checks the specific domain in the Return-Path.
