Summary
The question of whether aspf=strict SPF alignment provides significant deliverability benefits over aspf=relaxed is a common one in email deliverability. While strict alignment requires an exact match between the domain in the Return-Path (Mail-From) header and the From header domain, relaxed alignment permits a subdomain match. Most experts and marketers agree that for general email sending, aspf=relaxed is sufficient for DMARC alignment and provides little, if any, additional deliverability upside by switching to strict. Indeed, adopting a stricter alignment can introduce complexities and limit configuration options without substantial security gains against malicious actors.
Key findings
- No noticeable benefit: Many experienced professionals doubt there's a practical deliverability benefit to using aspf=strict over aspf=relaxed, particularly if current deliverability is strong.
- DMARC compliance: DMARC alignment is typically achieved with aspf=relaxed, which is the common standard most recipients expect and validate against. Learn more about DMARC tags and their meanings.
- Configuration limitations: Strict alignment can restrict your own email configuration options, potentially causing issues with third-party email service providers (ESPs) or complex sending infrastructures.
- Security impact: While strict alignment seems more secure, it doesn't necessarily add significant protection against bad actors using your domain, as DMARC's core enforcement handles this regardless of the alignment mode (provided it's implemented correctly). For a deeper understanding, explore relaxed DMARC vs. strict DMARC.
- Unforeseen impacts: Altering a well-performing email setup, even for seemingly minor authentication tweaks, can lead to unexpected negative consequences for deliverability.
Key considerations
- Current performance: If your deliverability is already good (e.g., high open rates, no DMARCian threats), there is little incentive to change your SPF alignment to strict.
- SPF -all vs ~all: Ensure your SPF record uses -all (fail) instead of ~all (softfail) for DMARC to effectively enforce policies. Otherwise, a softfail may not be treated as a pass by DMARC. Understand the implications of SPF ~all vs -all.
- Specific use cases: Strict alignment might only be considered in rare edge cases, such as when different divisions within a single company have distinct sending practices that require granular control and isolation.
What email marketers say
Email marketers often prioritize stability and measurable improvements. When it comes to SPF alignment, the consensus among many marketers is that adhering to aspf=relaxed is usually sufficient for achieving DMARC compliance and maintaining strong deliverability. They advise against making changes to a well-functioning email sending setup unless there's a clear, data-backed reason to do so, as seemingly small adjustments can lead to unforeseen negative impacts on inbox placement.
Key opinions
- Relaxed is standard: Many marketers view aspf=relaxed as the accepted and effective standard for DMARC alignment, providing sufficient security and deliverability without unnecessary complexity.
- If it ain't broke: There's a strong sentiment that if current email deliverability is good, marketers should avoid making changes to authentication settings that could inadvertently disrupt established sending reputation. This aligns with overall best practices for improving email deliverability.
- Focus on main domain: Marketers emphasize the importance of the Return-Path domain matching the main sending domain for proper SPF alignment and maintaining sender reputation, which is crucial for overall inbox placement. This is critical for avoiding DMARC, SPF, and DKIM alignment failures.
- DMARC enforcement: A robust DMARC policy with aspf=relaxed is generally effective for preventing unauthorized use of a domain, which is a key security concern for marketers.
Key considerations
- Data-driven decisions: Marketers should only consider shifting to aspf=strict if specific data or observable issues indicate that relaxed alignment is hindering deliverability or security goals.
- ESP compatibility: When using third-party ESPs, marketers must ensure that their Return-Path domain setup supports the desired SPF alignment mode. Many ESPs might default to relaxed alignment due to the complexities of strict matching.
- Return-Path management: A clear and organized Return-Path for bounced messages is vital for deliverability and maintaining sender reputation, irrespective of strict or relaxed alignment.
- Marketing benefits: Some marketers may consider stronger DMARC policies (which aspf=strict might imply as part of an overall posture) for benefits like Brand Indicators for Message Identification (BIMI) eligibility, which can display a certified logo next to emails. Read more about the benefits of a strong DMARC policy.
Email marketer from Email Geeks states that DMARC aligned is the standard everyone aims for, and that standard is usually achieved with aspf=relaxed.
Email marketer from Email Geeks suggests that if an organization is satisfied with their current deliverability, they should avoid changing their email sending configuration or seeking improvements without a clear need. A seemingly minor change could have unforeseen negative effects on deliverability.
What the experts say
Email deliverability experts generally advise caution when considering aspf=strict. They highlight that aspf=relaxed is perfectly adequate for DMARC alignment and enforcement in most scenarios, providing sufficient protection against impersonation. Experts suggest that strict alignment primarily restricts a sender's own configuration flexibility without providing a tangible uplift in security or deliverability for the majority of use cases. They often recommend against over-engineering authentication setups when simpler, effective solutions exist.
Key opinions
- Relaxed is sufficient: Experts largely concur that aspf=relaxed achieves the goal of DMARC alignment effectively and is the accepted industry standard.
- Limited security gain: Using aspf=strict (or adkim=strict) does not significantly enhance security against malicious actors compared to a well-implemented relaxed policy combined with DMARC enforcement.
- Configuration constraints: Strict alignment often imposes unnecessary constraints on a sender's legitimate email configurations, potentially leading to deliverability challenges when using subdomains or third-party sending services.
- SPF ~all vs -all: Experts confirm that a SPF softfail (~all) will not pass DMARC alignment, underscoring the importance of using -all for stronger enforcement. Learn more about why SPF passes in headers but not Google Postmaster Tools.
Key considerations
- Risk assessment: Before changing to strict alignment, conduct a thorough risk assessment. Unforeseen deliverability impacts, like increased bounces or messages landing in spam or junk folders, are a real possibility with such modifications.
- Trust within organization: Strict alignment might be considered only in specific organizational contexts, for example, when a company needs to tightly control email sending from various internal divisions and does not fully trust all sub-entities.
- Monitoring: Regardless of the chosen alignment mode, continuous DMARC monitoring is crucial to ensure email authentication is functioning as intended and to quickly identify any issues. Read about common pitfalls in DMARC configuration.
Deliverability expert from Email Geeks suggests that DMARC-aligned email is the expected norm and is typically achieved with aspf=relaxed, indicating that strict alignment offers no inherent additional advantage.
Deliverability expert from WordToTheWise.com often advises against unnecessary complexity in email authentication. They highlight that strict alignment can introduce more challenges than benefits for most senders, particularly those with diverse sending setups or third-party email providers.
What the documentation says
Official documentation and technical guides provide clear definitions of SPF alignment modes. They consistently describe aspf=strict as requiring an exact domain match and aspf=relaxed as permitting a parent/subdomain match. While strict offers tighter control, documentation implies that relaxed is a widely accepted and sufficient method for DMARC compliance, especially given the complexities of email ecosystems with various sending practices.
Key findings
- Definitions: Documentation defines aspf=s (strict) as requiring an exact match between the SPF-authenticated domain and the From header domain, while aspf=r (relaxed) allows a parent or subdomain match.
- DMARC integration: SPF alignment, whether strict or relaxed, is a key component of DMARC authentication, which helps verify sender legitimacy and prevents spoofing. Get a simple guide to DMARC, SPF, and DKIM.
- Return-Path domain: Successful SPF alignment depends on the Return-Path (or Mail-From) domain being consistent with the From header domain, which is essential for receivers to trust the sender.
- Combined authentication: Documentation emphasizes that the combination of SPF, DKIM, and DMARC provides a comprehensive email authentication framework. Understand Domain-Based Message Authentication.
Key considerations
- Practicality vs. strictness: While strict alignment provides granular control, many email sending scenarios (e.g., using ESPs with their own mail-from domains) necessitate relaxed alignment for successful DMARC validation.
- Policy choice: The choice between strict and relaxed SPF alignment should align with the overall DMARC policy goals and the sender's email infrastructure complexity. For example, safely transitioning DMARC policy often starts with monitoring.
- DMARC reports: Analyzing DMARC aggregate and forensic reports is crucial for understanding how different alignment modes are performing and if any legitimate email is failing authentication.
Documentation from DANAconnect explains that the aspf tag dictates SPF alignment, determining how the domain used for SPF verification relates to the domain in the From field of the email.
Documentation from Scaleway states that aspf=s (strict) mode for SPF alignment requires an exact match for authentication to pass.
