When implementing DMARC, a common point of confusion arises regarding which SPF identity DMARC checks should align with: the HELO domain or the Return-Path (also known as MAILFROM). This issue is compounded by the fact that some email security vendors may implement DMARC validation differently than what is commonly practiced or recommended by the DMARC specification. Simultaneously, there's a broader question of whether email authentication efforts should prioritize DKIM over SPF due to SPF's limitations with email forwarding and intermediary services.
Key findings
DMARC specification: RFC 7489, which defines DMARC, explicitly states that the HELO SPF identity is not typically used in the context of DMARC alignment. The focus for SPF alignment within DMARC is on the Return-Path domain.
Common practice: The vast majority of webmails and antispam solutions check SPF alignment against the MAILFROM domain, aligning with DMARC's intended operation. However, some vendors may diverge from this standard, causing legitimate emails to fail authentication.
DKIM's role: DKIM is generally considered a more robust authentication method for DMARC, especially given SPF's vulnerability to breaking when emails are forwarded or processed by intermediaries that alter the Return-Path. Strong DKIM implementation and alignment are crucial.
Vendor discrepancies: Email security vendors, like Trend Micro in some instances, may have proprietary implementations that check SPF alignment on the HELO domain, despite the sender having a robust DMARC configuration based on Return-Path and DKIM.
Key considerations
Prioritize DKIM: Given the potential for SPF to break due to forwarding or intermediary services, ensure your DKIM setup is robust and aligned. Learn more about how SPF, DKIM, and DMARC email authentication standards work.
DMARC alignment: When configuring DMARC, remember that SPF alignment primarily refers to the Return-Path domain aligning with the From: header domain, not necessarily the HELO domain. The SPF RFC itself covers both HELO and Return-Path, but DMARC's context is narrower.
Troubleshooting: If you encounter DMARC failures, investigate both SPF and DKIM authentication. Pay close attention to how specific receiving systems process these checks, especially if they deviate from common standards. For more details, consult a guide to SPF, DKIM, and DMARC implementation.
Vendor communication: If a vendor's DMARC implementation causes issues, engage their support with precise details, referencing relevant RFCs to highlight discrepancies. Sometimes, public discourse can also prompt changes, as seen with some blocklist operators.
Email marketers often face practical challenges when dealing with DMARC implementations, particularly when third-party services or email security gateways deviate from expected authentication behaviors. Their experiences highlight the real-world impact of technical configurations on email deliverability and business-critical communications. The emphasis shifts from theoretical RFC adherence to ensuring emails reliably reach the inbox.
Key opinions
Frustration with inconsistencies: Marketers are often frustrated when email security products claim to perform DMARC checks but do so incorrectly, such as prioritizing HELO alignment over MAILFROM for SPF.
Impact on critical emails: When legitimate, business-critical emails (e.g., support tickets) are blocked or quarantined due to misconfigured DMARC checks by a recipient's security solution, it creates significant operational hurdles.
Reliance on DKIM: There's a strong sentiment that DKIM should be the primary focus for DMARC alignment in modern email ecosystems, as it is generally more resilient to common email forwarding scenarios than SPF.
Vendor support challenges: Marketers frequently encounter unhelpful or unresponsive support from security vendors, who may insist on their proprietary methods even when they contradict industry standards.
Key considerations
DMARC policy application: Implementing a DMARC policy with p=reject or p=quarantine requires careful monitoring of DMARC reports to avoid legitimate email blockages. Learn more about implementing a DMARC policy.
Shared sending environments: When using third-party email service providers, marketers must ensure these providers handle SPF and DKIM alignment correctly on behalf of their domain, especially with regard to the From: header.
Troubleshoot DKIM first: If DMARC failures occur, prioritize checking DKIM alignment and signature validity, as it's often the more reliable authentication path. Refer to guides on troubleshooting DKIM and SPF settings.
Vendor negotiation: Marketers may need to directly engage their email security vendors or their sending service providers to resolve authentication discrepancies, often requiring persistence or escalation.
Marketer view
Marketer from Email Geeks explains they are struggling with an issue where Trend Micro is checking SPF alignment on the HELO domain instead of the MAILFROM domain for incoming DMARC checks, despite most webmails and antispam systems using MAILFROM.
03 Jul 2024 - Email Geeks
Marketer view
Marketer from Mxtoolbox Community discusses how misconfigured SPF records can cause emails to be soft-failed or even rejected, significantly impacting deliverability to recipients.
15 Feb 2024 - Mxtoolbox Community
What the experts say
Email deliverability experts consistently advocate for adherence to established RFCs while acknowledging the realities of diverse email system implementations. Their insights provide crucial guidance on prioritizing authentication methods and troubleshooting complex DMARC-related issues. The consensus leans towards a stronger reliance on DKIM for DMARC alignment due to SPF's inherent limitations.
Key opinions
DKIM over SPF for DMARC: Experts largely agree that for DMARC, DKIM alignment is more reliable and should be prioritized over SPF, especially considering SPF's fragility with forwarding paths.
Return-Path importance: In the context of DMARC, SPF validation should primarily focus on the Return-Path (MAILFROM) domain's alignment with the From: header, as opposed to the HELO domain.
Vendor resistance: Some security vendors are known to operate with non-standard interpretations of email authentication protocols, making it challenging to align with them through conventional means.
Solutions exist: Even when faced with difficult vendors, there are often alternative strategies, such as focusing on strong DKIM, adjusting DMARC policies (e.g., to quarantine), or escalating issues publicly.
Key considerations
DMARC policy options: For incoming emails, consider setting DMARC failures to quarantine rather than reject to allow for manual review of problematic senders, particularly critical third-party services. This is a common part of DMARC best practices.
Thorough testing: Before enforcing strict DMARC policies, test how different email security gateways handle your authenticated emails. This proactive step can identify potential issues. See our guide to SPF, DKIM, and DMARC.
Focus on root cause: When a DMARC failure occurs, identify whether SPF or DKIM is failing and investigate the specific reason (e.g., alignment issues, invalid signature, or policy misinterpretation).
Stay informed: Keep abreast of updates to email authentication standards and common practices from authoritative sources like DMARC.org or the IETF to best understand authentication requirements.
Expert view
Expert from Email Geeks suggests exploring why an aligned DKIM domain might not be signing correctly before focusing solely on SPF issues, as DKIM is often the more reliable indicator.
03 Jul 2024 - Email Geeks
Expert view
Expert from Spam Resource emphasizes that DMARC's primary goal is to enforce alignment, and both SPF and DKIM must align with the From: header domain for successful validation.
01 Jun 2024 - Spam Resource
What the documentation says
Official documentation and RFCs provide the foundational understanding for email authentication protocols. While these documents define the technical specifications, their interpretation and implementation by various systems can sometimes vary. It is essential to refer to these authoritative sources to understand the intended behavior of SPF, DKIM, and DMARC.
Key findings
RFC 7489 (DMARC): The DMARC specification clearly states that the SPF identity based on the HELO domain is not typically used for DMARC alignment purposes, prioritizing the MAILFROM identity.
RFC 7208 (SPF): The SPF specification allows for checks against both the HELO identity and the MAIL FROM identity. However, DMARC introduces an additional alignment requirement.
DMARC alignment requirement: For DMARC to pass via SPF, the domain in the Return-Path must align with the domain in the From: header.
DKIM alignment: For DMARC to pass via DKIM, the domain specified in the DKIM-Signature header's d= tag must align with the From: header domain.
Key considerations
RFC adherence: Organizations should primarily configure their outbound email systems to comply with DMARC's specific alignment requirements for SPF (Return-Path) and DKIM (d= tag), as detailed in RFC 7489.
Inbound DMARC validation: Receiving systems performing DMARC checks should primarily validate SPF alignment against the MAILFROM domain and not solely on the HELO domain, to correctly interpret DMARC policies.
Vendor documentation vs. practice: It is crucial to compare a vendor's documented DMARC behavior with its actual implementation, as discrepancies can lead to unexpected authentication failures. For example, Trend Micro's documentation outlines MailFrom checks for SPF.
Comprehensive authentication: While SPF and DKIM can function independently, DMARC unifies them by adding an alignment requirement, making a combination of all three the strongest approach for email authentication and spam protection.
Technical article
Documentation from RFC 7489 (DMARC) specifies that the HELO SPF identity is not typically used in the context of DMARC alignment checks, emphasizing the importance of the 'MAIL FROM' identity instead.
01 Jan 2020 - RFC 7489
Technical article
Documentation from RFC 7208 (SPF) outlines that an SPF check can authenticate either the HELO identity or the MAIL FROM identity, offering flexibility in its application before DMARC alignment is considered.