What could cause Gmail SPF/DKIM issues and how to check authentication results in email headers?

Key findings

• Impact on deliverability: Zero percent SPF/DKIM reporting in Google Postmaster Tools often correlates directly with abysmal open rates and emails going to spam.
• DNS dependencies: Major DNS provider outages, such as those impacting Cloudflare, can indirectly cause SPF and DKIM issues by making DNS records temporarily unreachable. For more on this, read our guide on troubleshooting intermittent delivery failures.
• Header diagnostics: Email headers, particularly the Authentication-Results section, contain vital diagnostic information about SPF, DKIM, and DMARC authentication outcomes.
• Beyond PASS: An email showing PASS for SPF, DKIM, and DMARC in its headers can still land in spam due to other factors like content, sender reputation, or recipient engagement. You can learn more about this in our overview of email authentication.

Key considerations

• Monitor actively: Regularly check Google Postmaster Tools for any anomalies in your SPF and DKIM authentication rates. Sudden drops indicate an issue.
• Distinguish outage types: Determine if issues are due to your DNS provider, your email service provider, or a broader issue with a receiving mailbox provider like Gmail.
• Verify DNS health: Ensure your DNS records for SPF and DKIM are correctly published and resolving properly, especially after any infrastructure changes or outages. Our guide explains SPF, DKIM, and DMARC basics.
• Examine headers carefully: When troubleshooting, obtain the full email headers from a problematic message (preferably sent to a personal Gmail account) to analyze the authentication results directly.
• Avoid false positives: Internal whitelisting of IPs can mask deliverability issues, so testing with external, unwhitelisted accounts is crucial for an accurate assessment.

Key opinions

• Sudden performance drops: Marketers frequently notice an immediate and severe impact on email campaign performance, such as a drastic drop in open rates, which signals authentication problems.
• Postmaster Tools concerns: Reports of 0% SPF/DKIM authentication in Google Postmaster Tools are a major red flag, prompting urgent investigation.
• DNS outage suspicion: External events like widespread DNS provider outages are often the first suspected culprits for sudden authentication failures.
• Personal account testing: Marketers resort to sending emails to personal Gmail accounts to verify if messages are indeed landing in spam, bypassing internal whitelists.
• Header inspection importance: Analyzing email headers is seen as a crucial step for diagnosing authentication issues, even if the initial results appear to be passing. Our guide on why your emails go to spam can offer more insight.

Key considerations

• Initial diagnosis: How can marketers quickly determine if a reported issue is an isolated incident or a broader, systemic problem affecting more senders?
• Understanding header nuances: What specific header fields, beyond Authentication-Results, should marketers examine for more granular insights into deliverability issues? For more on DMARC failures, see our guide on how to fix DMARC fail errors.
• Impact of whitelisting: Recognizing that internal IP whitelisting can obscure actual deliverability problems, making testing on external accounts indispensable.
• Resolving misconfigurations: How should marketers approach troubleshooting SPF or DKIM issues when their Postmaster Tools reports show 0% authentication, but headers show PASS? This issue is explored further in our article on why emails get blocked by Gmail.
• Root cause analysis: Investigating potential causes beyond immediate authentication results, such as content issues, reputation, or list quality, when emails still land in spam.

Key opinions

• Systemic issues are rare: It is uncommon for Gmail to experience widespread, systemic authentication issues affecting all senders simultaneously. Problems are often specific to individual configurations.
• Header analysis is key: The most effective way to diagnose an authentication failure is by reviewing the full email headers for specific diagnostics, particularly the Authentication-Results section. Sweego provides a helpful guide on how to analyze email headers.
• Whitelisting can obscure: Relying on internal Gsuite accounts with whitelisted IPs can give a false sense of security regarding deliverability, as it bypasses real-world spam filtering.
• Beyond PASS for spam: Even if SPF, DKIM, and DMARC show a PASS, other factors such as sender reputation, content, or recipient engagement can cause emails to land in spam. For more on this, see our article on how to troubleshoot Gmail spam issues.

Key considerations

• Holistic view: Adopt a holistic approach to deliverability, understanding that authentication is a critical component but not the sole determinant of inbox placement.
• Proactive monitoring: Implement robust monitoring for DNS changes and authentication results, beyond just relying on Postmaster Tools, which may not provide real-time granular data. Our guide on troubleshooting DMARC reports can assist.
• Deep dive into headers: Learn to interpret specific values within the Authentication-Results header, as they provide detailed reasons for SPF or DKIM failures, or even successful passes. For more on this, read how to fix SPF and DMARC settings.
• Understanding DMARC: Familiarize yourself with DMARC policies and how they interact with SPF and DKIM results, as a failure in either can lead to DMARC enforcement actions like quarantine or rejection.

Key findings

• SPF validation: Sender Policy Framework (SPF) verifies that the sending IP address is authorized to send emails on behalf of a domain. Our full form of SPF in email article provides further context.
• DKIM signatures: DomainKeys Identified Mail (DKIM) adds a digital signature to emails, allowing recipients to verify the message's authenticity and integrity, ensuring it hasn't been tampered with in transit.
• DMARC policy: Domain-based Message Authentication, Reporting, and Conformance (DMARC) instructs receiving servers on how to handle emails that fail SPF or DKIM, based on published policies.
• Authentication-Results header: The Authentication-Results header field summarizes the authentication checks performed by the receiving Mail Transfer Agent (MTA), including SPF, DKIM, and DMARC. Sweego provides an excellent overview on analyzing email authentication headers.
• ARC for forwarded mail: Authenticated Received Chain (ARC) is designed to preserve authentication results across trusted intermediaries, such as mailing lists or forwarders, that might otherwise break SPF or DKIM signatures. You can learn more about ARC in this article on ARC from DuoCircle.

Key considerations

• DNS record accuracy: Ensure your SPF and DKIM DNS records are correctly formatted and published, as errors here are a common cause of authentication failures.
• Alignment requirements: Understand the concept of DMARC alignment, where the SPF and DKIM authenticated domains must align with the From: domain in the email header.
• DKIM signature integrity: Be aware that any modification to an email's headers or body after it has been DKIM-signed can invalidate the signature, leading to a DKIM failure. If you're experiencing this, review our guide on decoding DKIM temperror.
• Interpreting results: Learn to interpret the different states reported in the Authentication-Results header (e.g., pass, fail, softfail, none, temperror) to accurately diagnose issues.