Is Google applying SPF checks to EHLO values for stricter email authentication?
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Apr 2025
Updated 16 Aug 2025
10 min read
Email authentication has become increasingly critical for deliverability, with major inbox providers like Google and Yahoo implementing stricter guidelines. A recurring question among email senders is whether Google is applying SPF checks to EHLO values for stricter email authentication, moving beyond just the MAIL FROM identity. This topic often leads to confusion, given the nuances of SMTP protocol and how different parts of an email are authenticated.
The distinction between EHLO/HELO and MAIL FROM in the context of SPF is significant. While SPF primarily authenticates the MAIL FROM domain (also known as the Return-Path or Envelope From), there's a recommended practice to also check the EHLO/HELO identity. Understanding if and how Google utilizes this for its stricter policies is key to maintaining high deliverability rates.
Sender Policy Framework (SPF) is designed to prevent email spoofing by allowing domain owners to publish a DNS record that lists which mail servers are authorized to send email on their behalf. When a receiving mail server gets an email, it checks the SPF record of the sending domain to verify the sender's legitimacy. This check traditionally focuses on the MAIL FROM address, which is specified in the email's envelope during the SMTP transaction.
However, the SPF specification (RFC 7208 section 2.3) explicitly states that verifiers are RECOMMENDED to check both the MAIL FROM identity and the HELO (or EHLO) identity. The EHLO/HELO command is the first command sent by the client to the server in an SMTP conversation, identifying the client's hostname. Checking the HELO domain can promote consistency and reduce DNS resource usage if a conclusive determination can be made early.
While the specification recommends checking both, many mail receivers historically prioritize the MAIL FROM domain for SPF evaluation, especially in scenarios where a clear SPF record exists for it. However, in cases where the MAIL FROM is absent (e.g., in bounce messages with an empty Return-Path), the receiving server may fall back to using the HELO/EHLO domain for SPF validation. This subtle but important detail highlights why proper configuration of both domains is essential for robust email authentication.
Google, alongside Yahoo, has recently rolled out new email sender guidelines aimed at enhancing email security and combating spam. These policies emphasize the mandatory implementation of SPF, DKIM, and DMARC for all bulk senders. While Google's primary focus for SPF checks remains the MAIL FROM domain, their general move towards stricter authentication suggests that all aspects of email authenticity are under increased scrutiny.
Their official email sender guidelines recommend setting up SPF, DKIM, and DMARC to improve email delivery. This implies a comprehensive approach where a strong alignment across all authentication methods contributes to positive sender reputation. Although they might not explicitly state stricter SPF checks on EHLO values, any authentication failure, regardless of the specific identifier, can negatively impact deliverability.
The objective of these updated policies is to minimize spam, phishing, and spoofing. By requiring senders to authenticate their emails, Google enhances trust in the email ecosystem. Senders who fall short of these requirements are likely to see their emails delivered to spam folders or even rejected outright. This broad enforcement makes it prudent to ensure all aspects of your email authentication, including the HELO/EHLO domain's SPF record, are correctly configured.
Google's email authentication requirements
Mandatory authentication: All senders must set up SPF, DKIM, and DMARC for their sending domains.
Alignment focus: While MAIL FROM SPF is key, strong authentication results across all standards contribute to positive reputation.
Reputation impact: Lack of proper authentication can lead to emails landing in spam or being rejected, affecting domain reputation.
The practical impact of EHLO SPF checks
While most Email Service Providers (ESPs) and mail receivers primarily use the MAIL FROM identity for SPF checks, some may indeed check the HELO/EHLO domain, especially if the MAIL FROM domain lacks a clear SPF record or if they are implementing very strict anti-spoofing measures. DMARC aggregate reports can sometimes offer clues through the <spf_scope>field, which indicates whether the SPF check was performed against the mfrom (MAIL FROM) or helo (EHLO/HELO) identity.
For email senders, this means that merely having a valid SPF record for your MAIL FROM domain might not always be enough, especially if you are seeing deliverability issues with Google. Ensuring that the domain used in your EHLO/HELO command also has a properly configured SPF record is a best practice that can help prevent potential problems, particularly with more discerning mail providers.
It is crucial for Email Service Providers to manage HELO, rDNS, and SPF properly, as inconsistencies can lead to authentication failures. Even if the SPF record for the EHLO domain is not strictly enforced, its absence or misconfiguration can contribute to a lower overall trust score, impacting your email's journey to the inbox. This comprehensive approach to authentication (including DMARC and DKIM) ensures that Google and other providers recognize your emails as legitimate.
Focus on MAIL FROM (Traditional)
Primary identity: SPF check usually performed against the Return-Path or Envelope From address.
Widespread adoption: Most mail servers and Google traditionally prioritize this for SPF.
DMARC reports: SPF authentication results in DMARC aggregate reports often show spf_scope as mfrom.
Focus on EHLO (Stricter Approach)
Secondary identity: Checked when MAIL FROM is absent or as an additional security layer.
RFC recommendation: The SPF specification recommends checking HELO/EHLO first.
Emerging trend: Stricter policies from major providers might increase reliance on HELO/EHLO validation.
The role of PTR records and reverse DNS
Beyond SPF and DKIM, another critical factor influencing email deliverability, especially with Google, is the correct configuration of Reverse DNS (PTR) records. A PTR record maps an IP address back to a domain name, essentially the reverse of a standard DNS A record. It provides a layer of verification that the IP sending the email is indeed associated with the domain it claims to be from.
Google and other major mail providers use PTR records and HELOs to impact email deliverability as part of their anti-spam efforts. If a sending IP address's PTR record points to a hostname that results in an NXDomain (Non-Existent Domain) error, it signals a potential misconfiguration or suspicious activity. Such inconsistencies can significantly undermine your sender reputation and lead to emails being blocked or flagged as spam, even if your SPF and DKIM are otherwise sound.
For senders using smaller IP ranges (like a /27 subnet) from a hosting provider, ensuring a correctly configured PTR record becomes even more vital. Some providers, including Google, might view emails from such IPs with more scrutiny if basic authentication signals like reverse DNS are absent or incorrect. Fixing PTR issues is often considered low-hanging fruit in improving deliverability, as it affects not only Google but also other major inbox providers like Microsoft and even smaller mail servers running spam filters.
It is not just about SPF and DKIM, but a holistic approach to email authentication that includes PTR records, monitoring blocklists, and maintaining a strong sender reputation across the board. Addressing these fundamental DNS aspects helps establish trust and ensures your emails reach their intended recipients rather than being caught by spam filters or being put on an email blacklist.
Ensuring comprehensive email authentication for Google
To ensure your emails are consistently delivered to Google inboxes, a multi-faceted approach to email authentication is necessary. While the direct impact of stricter SPF checks on EHLO values from Google is not always explicitly detailed, the underlying principle is clear, authenticate everything. Any element that contributes to the authenticity of a sending domain and IP address should be properly configured and regularly monitored.
This includes not only your SPF record for both MAIL FROM and EHLO domains, but also your DKIM signatures and DMARC policy. Regularly reviewing DMARC reports can provide insights into how different receivers are evaluating your authentication, including the spf_scope to see if EHLO is being considered. Additionally, maintaining proper PTR records for your sending IPs is a foundational requirement that helps establish trustworthiness with all major inbox providers.
Ultimately, the goal is to present a consistent and verifiable identity across all stages of the email sending process. By proactively addressing these authentication elements, senders can significantly improve their email deliverability and avoid common pitfalls that lead to emails being flagged as spam or rejected. The evolving landscape of email security demands constant vigilance and adherence to best practices, not just minimum requirements.
Views from the trenches
Best practices
Always publish SPF records for both your MAIL FROM and HELO/EHLO domains to cover all bases.
Regularly monitor your DMARC aggregate reports to understand how receivers are interpreting your authentication.
Ensure that your sending IP addresses have correct PTR records that resolve back to legitimate hostnames.
Consistently apply SPF, DKIM, and DMARC across all your sending systems and third-party services.
Common pitfalls
Neglecting to publish an SPF record for the HELO/EHLO domain, leading to potential warnings or rejections.
Assuming that passing SPF on MAIL FROM is sufficient without considering other authentication factors.
Having misconfigured PTR records, which can severely impact domain reputation and deliverability.
Ignoring DMARC aggregate reports, missing crucial insights into authentication failures and compliance.
Expert tips
Even if Google doesn't explicitly penalize EHLO, a clean record shows diligence and builds trust.
Think of authentication as a layered security approach, each layer strengthens your sender profile.
Automate monitoring of SPF, DKIM, DMARC, and PTR records to catch issues before they impact deliverability.
Engage with your email service provider to ensure they support and correctly implement all authentication standards.
Expert view
Expert from Email Geeks says that the SPF specification recommends checking HELO before MAIL FROM if both are checked, although it doesn't prioritize if both pass.
2024-03-08 - Email Geeks
Marketer view
Marketer from Email Geeks says that DMARC aggregate reports, particularly the spf_scope, can reveal whether receivers are looking at the MAIL FROM or EHLO domain during SPF checks, and it's usually the MAIL FROM.
2024-03-08 - Email Geeks
Key takeaways for senders
While Google's new email authentication requirements primarily focus on robust SPF, DKIM, and DMARC for the MAIL FROM domain, it's clear that the broader context of email authentication is evolving. The SPF specification's recommendation to check the HELO/EHLO identity indicates that some receiving mail servers may indeed use this for stricter validation, especially in scenarios where the primary MAIL FROM SPF check is inconclusive or absent.
For senders, this underscores the importance of a comprehensive approach to email authentication. Beyond ensuring your SPF, DKIM, and DMARC are correctly set up and aligned for your MAIL FROM domain, it's also prudent to ensure your EHLO/HELO domain has a valid SPF record. Additionally, the foundational element of a correctly configured PTR record for your sending IP addresses cannot be overstated, as it builds trust with all major mail providers, including Google.
By proactively addressing all these authentication signals, you can significantly enhance your email deliverability, reduce the likelihood of your emails being flagged as spam, and navigate the increasingly stringent landscape of email security with confidence.
Google traditionally prioritize this for SPF.
Microsoft and even smaller mail servers running spam filters.
