Suped
Is Google applying SPF checks to EHLO values for stricter email authentication?
Summary
The consensus is that while Google's specific implementation isn't explicitly confirmed, applying SPF checks to EHLO values is a potential component of stricter email authentication. This is driven by a combination of factors including reported tightening of authentication requirements, the SPF specification recommending HELO checks, and the increasing importance of DMARC. Though MAIL FROM remains the primary focus for many ESPs, EHLO checks can serve as an early filter and are influenced by domain reputation. The use of proper PTR records, and generally, fully configuring the infrastructure correctly is emphasized. HELO checking's utilization varies from system to system.

Key findings

  • Authentication Tightening: Reports suggest Google might be tightening authentication, potentially including stricter EHLO/FcrDNS checks.
  • SPF Spec Recommendation: The SPF specification recommends checking HELO before MAIL FROM.
  • HELO Implementation Variation: EHLO checks are not universally enforced; implementation varies across ESPs, with MAIL FROM often prioritized.
  • DMARC's Influence: DMARC indirectly elevates the importance of SPF HELO checks due to domain alignment requirements.
  • PTR Record Importance: Proper PTR records are essential for general deliverability.
  • Early filtering: HELO/EHLO checks are sometime utilized as an early filter.

Key considerations

  • Monitor Authentication Trends: Continuously monitor changes in authentication requirements and adapt accordingly.
  • Ensure Proper SPF Implementation: Implement SPF correctly, considering HELO checks, based on receiver requirements.
  • Verify Infrastructure: Verify that the HELO/EHLO domain is a valid, resolvable hostname and the infrastructure is completely and correctly configured.
  • Align with DMARC: Adhere to DMARC requirements for improved deliverability.
  • Evaluate ESP Practices: Understand whether your ESP prioritizes HELO or MAIL FROM SPF checks.
What email marketers say
13 marketer opinions
The question of whether Google is applying SPF checks to EHLO values for stricter email authentication is complex. While the RFC specification recommends HELO identity checks, implementations vary. Some email providers prioritize HELO checks, particularly for initial connections or when MAIL FROM records are absent. The growing importance of DMARC may indirectly increase the relevance of HELO checks. Some older systems strictly adhere to HELO checks, while many modern ESPs primarily focus on MAIL FROM. Not all ESPs implement HELO SPF checks, but those that do may use it as an early filter to reduce resource usage or improve domain reputation. Fixing PTR records remains a crucial step in improving email deliverability.

Key opinions

  • RFC Recommendation: RFC 7208 recommends checking HELO identity before MAIL FROM for consistency and reduced DNS resource usage.
  • Implementation Variance: HELO SPF checks are not universally enforced and implementation varies across ESPs; some prioritize HELO, others MAIL FROM.
  • DMARC Impact: DMARC’s requirement for domain alignment can indirectly increase the importance of HELO SPF checks.
  • Early Filtering: Some systems use HELO/EHLO checks as an initial filter to reject mail before checking MAIL FROM, saving resources.
  • PTR Records Importance: Maintaining correct PTR records is essential for general email deliverability and authentication.

Key considerations

  • Evaluate ESP Practices: Understand whether your ESP prioritizes HELO or MAIL FROM SPF checks and adjust your authentication strategy accordingly.
  • Monitor Authentication Reports: Regularly check SPF aggregate reports to understand which authentication scopes are being evaluated by receivers.
  • Implement Comprehensive Authentication: Ensure SPF records are properly configured and align with DMARC requirements to maximize deliverability.
  • Optimize SMTP Configuration: Verify that the HELO/EHLO domain is a valid, resolvable hostname to prevent deliverability issues.
  • Prioritize Reputation: Focus on maintaining a positive domain reputation through consistent authentication practices and responsible sending behavior.
Marketer view
Marketer from Email Geeks confirms that checking HELO before MAIL FROM is recommended but doesn't imply priority if both have valid SPF records, quoting RFC7208.
13 Mar 2025 - Email Geeks
Marketer view
Email marketer from Litmus states SPF and other authentication methods are important for getting to the inbox. EmailOnAcid further suggests that stricter adherence might include HELO checks.
13 Dec 2024 - Litmus
What the experts say
5 expert opinions
The possibility of Google applying SPF checks to EHLO values for stricter email authentication is debated. There are reports of Google tightening authentication requirements, leading to speculation about increased scrutiny of EHLO values and FcrDNS. The SPF specification mandates checking EHLO before MAIL FROM, but implementations vary. An authentication issue to be aware of is the PTR record showing a hostname that results in NXDomain, potentially impacting deliverability. In the age of DMARC, SPF HELO checks are becoming more relevant due to domain alignment requirements. While MAIL FROM remains the primary focus, HELO/EHLO checks can still impact deliverability, and a valid, resolvable hostname in HELO is crucial.

Key opinions

  • Google's Authentication: There are indications Google is tightening authentication requirements, possibly including stricter EHLO/FcrDNS checks.
  • SPF Specification: The SPF specification mandates checking EHLO before MAIL FROM, though implementation differs.
  • PTR Record Importance: A failing PTR record (hostname resulting in NXDomain) is an authentication issue that can impact deliverability.
  • DMARC's Influence: DMARC indirectly increases the relevance of SPF HELO checks due to domain alignment requirements.
  • HELO Hostname Validity: A valid, resolvable hostname in HELO is crucial for avoiding deliverability issues.

Key considerations

  • Monitor Authentication: Continuously monitor changes in Google's authentication practices and adapt accordingly.
  • Implement SPF Correctly: Ensure proper SPF implementation, including considerations for HELO checks, based on receiver requirements.
  • Verify PTR Records: Regularly check and ensure PTR records are correctly configured to avoid authentication failures.
  • Align with DMARC: Adhere to DMARC requirements and ensure domain alignment for improved email deliverability.
  • Validate HELO Hostname: Ensure a valid, resolvable hostname is used in HELO/EHLO to prevent negative impacts on deliverability.
Expert view
Expert from Email Geeks mentions that the SPF spec dictates checking EHLO before Mail From.
2 Jan 2024 - Email Geeks
Expert view
Expert from Word to the Wise indicates that while MAIL FROM is the primary focus, HELO/EHLO checks do happen, and a mismatch or failure can impact deliverability. Word to the Wise stresses the HELO must be a valid, resolvable hostname.
9 Feb 2024 - Word to the Wise
What the documentation says
5 technical articles
Documentation from various sources outlines the use of SPF records in email authentication. The IETF recommends checking the HELO identity for consistency and resource efficiency. While Google, Microsoft, Dmarcian, and SparkPost emphasize the importance of SPF in preventing unauthorized messages and validating message origin, they do not explicitly confirm Google's use of SPF checks on EHLO values. These resources imply that stricter SPF adherence and comprehensive authentication setups, which *may* include HELO analysis, are increasingly important for deliverability.

Key findings

  • IETF Recommendation: IETF documentation recommends SPF verifiers check the HELO identity.
  • SPF's Primary Purpose: SPF records help prevent unauthorized use of a domain by spammers.
  • Sender IP Verification: SPF aims to validate the sender's IP address, which is relevant to HELO/EHLO evaluation.
  • Implicit HELO Analysis: Documentation emphasizes SPF implementation, suggesting stricter adherence might incorporate HELO checks.
  • Comprehensive Authentication: All documentation leads to the thought that full email authentication is increasingly important for deliverability.

Key considerations

  • HELO's Value: Consider HELO identity checks, as recommended by the IETF, for enhanced authentication.
  • Sender's IP: Focus on ensuring that the sender's IP address is accurately represented in SPF records.
  • Evaluate SPF configuration: Implement stricter SPF adherence to help deliverability.
  • Focus on the whole picture: Know that email authentication is becoming increasingly complex, so focus on the whole picture, not just small aspects.
Technical article
Documentation from SparkPost explains that SPF records validate the sending server's IP. While it doesn't explicitly mention HELO, their documentation encourages a thorough SPF setup which implies the possibility of stricter HELO checking.
4 Apr 2024 - SparkPost
Technical article
Documentation from Microsoft Learn details that SPF records help validate the origin of email messages. While it doesn’t explicitly mention HELO checks, it emphasizes the importance of SPF in general, hinting that stricter adherence might include HELO checks as part of overall authentication.
20 Jul 2021 - Microsoft Learn
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