Summary
Gmail SPF/DKIM issues arise from various configuration errors and external factors. SPF problems include incorrect syntax, exceeding DNS lookup limits, not including all sending sources, SPF Permerror, and 'Hard Fail' results leading to spam filtering, or an SPF 'Neutral' result from unauthorized IPs. DKIM issues stem from incorrect key lengths, DNS record problems, a mismatch between keys, or incorrect DKIM selectors. Being on a blocklist can trigger spam filters. While systemic Google issues are rare, analyzing email headers for the 'Authentication-Results' section (as defined by RFC standards) helps diagnose problems, including checking disposition/reason codes. This header allows users to check the DKIM, SPF and DMARC results, including pass/fail states.
Key findings
- SPF Configuration: Issues include syntax errors, DNS lookup limits, incomplete sender lists, Permerror, and 'Hard Fail' results.
- DKIM Configuration: Errors include incorrect key lengths, DNS record problems, and mismatched keys.
- External Factors: Being on a blocklist can trigger Gmail's spam filter.
- Header Analysis: 'Authentication-Results' header (defined by RFC) provides valuable authentication details.
- Authentication Results: Authentication results shows breakdown of authentication checks.
Key considerations
- Audit SPF Records: Regularly check SPF records for syntax, limits, and complete sender lists.
- Verify DKIM Setup: Confirm DKIM key lengths, DNS records, and matching keys are correct.
- Monitor Blocklists: Ensure your IP is not on any blocklists.
- Analyze Headers: Review the 'Authentication-Results' header for detailed diagnostic information and ensure correct DKIM key selectors.
- Implement DMARC: If there is an SPF Hard Fail then Gmail is more likely to send it to spam.
What email marketers say
9 marketer opinions
Several factors can cause Gmail SPF/DKIM issues. SPF failures often stem from incorrect syntax in the SPF record, exceeding DNS lookup limits, the sender's IP not being included in the SPF record, or a 'Hard Fail' due to third-party senders not being authorized. DKIM problems arise from misconfigured DNS records, incorrect key selectors, or the DKIM key not matching the public key. Additionally, being on a blocklist can trigger Gmail's spam filter. To check authentication results, analyze email headers for the 'Authentication-Results' section to find SPF, DKIM, and DMARC pass/fail status and error details.
Key opinions
- SPF Configuration: Incorrect SPF syntax, DNS lookup limits, and missing sender IPs are common causes of SPF failures.
- DKIM Configuration: Incorrect DKIM DNS records or mismatched keys between the sender and DNS can cause DKIM failures.
- Blocklists: Being on a blocklist can lead to emails being marked as spam by Gmail, impacting SPF/DKIM checks.
- Header Analysis: The 'Authentication-Results' section in email headers provides valuable insights into SPF, DKIM, and DMARC checks.
Key considerations
- Audit SPF Records: Regularly audit your SPF records to ensure correct syntax, inclusion of all sending sources, and adherence to DNS lookup limits.
- Verify DKIM Setup: Double-check your DKIM DNS record and key selector to ensure they are correctly configured and up-to-date.
- Monitor Blocklists: Monitor your IP address for inclusion on any blocklists and take steps to be removed if listed.
- Analyze Authentication Results: Consistently analyze email headers to understand the outcome of SPF, DKIM, and DMARC checks and identify potential issues.
- Third Party Senders: If you use third-party senders include them in your SPF record.
Marketer view
Email marketer from EmailGeeks forum explains that the Authentication-Results show the breakdown of the email check, and a fail means that the email has failed the check and there is likely an error somewhere in the DKIM or SPF configuration.
19 Sep 2023 - EmailGeeks
Marketer view
Email marketer from Mailhardener explains that an SPF Permerror can occur due to syntax errors or exceeding DNS lookup limits. They advise auditing your SPF record to resolve.
17 Jan 2023 - Mailhardener
What the experts say
5 expert opinions
Gmail SPF/DKIM issues can stem from DNS lookup limits, syntax errors, and misconfigured includes in SPF records, leading to authentication failures. However, systemic Google-side problems are rare. The 'Authentication-Results' header, found in email headers, provides insights into SPF, DKIM, and DMARC checks, including disposition/reason codes for further analysis.
Key opinions
- SPF Configuration: DNS lookup limits, syntax errors, and misconfigured includes in SPF records are common issues.
- Non-Systemic Issues: Major systemic issues with Gmail SPF/DKIM are infrequent.
- Authentication-Results Header: This header provides valuable information about SPF, DKIM, and DMARC checks.
- Detailed Analysis: Disposition and reason codes within the Authentication-Results header offer further insights into authentication failures.
Key considerations
- Check SPF Records: Ensure your SPF records are correctly configured and adhere to DNS lookup limits.
- Investigate Failures: If authentication fails, thoroughly examine the disposition and reason codes in the Authentication-Results header.
- Monitor for Systemic Issues: While uncommon, monitor for any widespread Gmail SPF/DKIM issues.
- Locate Headers: Locate the authentication results by searching 'Authentication Results' in the email headers.
Expert view
Expert from SpamResource explains that common SPF issues include DNS lookup limits, syntax errors and misconfigured include mechanisms, and these can cause authentication to fail and emails to bounce or be filtered.
26 Jan 2025 - SpamResource
Expert view
Expert from Email Geeks provides an example of what the "Authentication-Results" section looks like in the email header.
4 Jan 2022 - Email Geeks
What the documentation says
5 technical articles
Gmail SPF/DKIM issues can stem from various configuration problems. SPF errors arise from incorrect syntax, exceeding the 10 DNS lookup limit, not including all sending sources, or a 'Neutral' result indicating the domain owner hasn't authorized the sending IP. DKIM problems can be caused by incorrect key length or issues with DNS records. Authentication results, found in email headers, can be used to check the DKIM, SPF and DMARC results, including pass/fail states.The Authentication-Results header's structure and meaning are defined in RFC standards.
Key findings
- SPF Configuration Issues: Incorrect syntax, DNS lookup limits, and incomplete sender lists are common SPF errors.
- DKIM Configuration Issues: Incorrect key length or problems with DNS records are potential DKIM issues.
- SPF Neutral Result: An SPF 'Neutral' result indicates the domain owner hasn't explicitly authorized the sending IP, affecting deliverability.
- Authentication Header: Email authentication results are found in the headers.
- Authentication Standard: The 'Authentication-Results' header is standardized as per RFC.
Key considerations
- Validate SPF Records: Ensure SPF records are correctly configured, include all sending sources, and adhere to DNS lookup limits.
- Verify DKIM Setup: Check DKIM key length and DNS records for accuracy, potentially using a DKIM validator.
- Avoid Neutral SPF: Explicitly authorize sending IPs in your SPF record to avoid a 'Neutral' result.
- Utilize Authentication Header: Analyze email headers, find authentication results and check DKIM, SPF and DMARC results.
- Reference RFC: Consult RFC standards for a detailed understanding of the Authentication-Results header.
Technical article
Documentation from RFC explains the structure and meaning of the 'Authentication-Results' header field, used to report the results of SPF, DKIM, and other authentication methods.
14 Oct 2023 - RFC
Technical article
Documentation from dmarcian explains how to find authentication results, in the email header. They also explain how to read the DKIM, SPF and DMARC results, including pass/fail states.
8 Mar 2022 - dmarcian
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