Summary
Dips in SPF authentication rates within Google Postmaster Tools are multifactorial, stemming from configuration errors in SPF records (syntax errors, exceeding DNS lookup limits, incomplete inclusion of sending IPs), reliance on third-party senders or ESPs without proper SPF authorization, domain spoofing or unauthorized sending, DNS resolution issues, IP reputation challenges, incorrect SPF alignment, and shared IP environments where the actions of other users impact authentication. Even with DMARC in place, SPF failures degrade sender reputation and deliverability.
Key findings
- Configuration Errors: Incorrect syntax, exceeding DNS lookup limits, and not including all sending IPs in SPF records are common mistakes causing dips.
- Third-Party Issues: Using third-party senders (ESPs, CRMs) without proper authorization in the SPF record is a significant contributor to SPF failures.
- DNS and Network Problems: Temporary DNS resolution issues can cause intermittent SPF failures, leading to short-term dips in authentication rates.
- IP Reputation Effects: Low IP reputation, especially on shared IPs, impacts SPF authentication rates, making checks less reliable.
- SPF Alignment Importance: Google Postmaster Tools considers SPF alignment similar to DMARC. SPF success is not just about passing the SPF check, but that SPF must be aligned with the 'Mail From' domain. Discrepancies between the domain used for DKIM and the domain used for SPF will cause Authentication issues.
- Impact on Deliverability: Authentication issues will have a negative impact on sender reputation and deliverability.
Key considerations
- Regular SPF Monitoring: Continuously monitor SPF records for errors, unintended changes, and the need to include new sending sources.
- Authorize All Senders: Ensure all sending sources (third-party services, CRMs, etc.) are properly authorized in the SPF record.
- Flatten SPF Records: Consider SPF flattening to avoid exceeding DNS lookup limits when using multiple 'include:' mechanisms.
- Address DNS and Network Problems: Investigate and resolve any DNS resolution issues that may cause intermittent SPF failures.
- Improve IP Reputation: Monitor and improve IP reputation, particularly on shared IPs, to enhance SPF authentication rates.
- Testing and validation: Regularly test and validate your SPF records to ensure they are working as expected by using SPF testing tools.
What email marketers say
12 marketer opinions
Dips in SPF authentication rates in Google Postmaster Tools can be attributed to several factors. These include misconfigurations in SPF records (e.g., syntax errors, exceeding DNS lookup limits, not including all sending IPs), the use of third-party senders or CRMs without proper SPF authorization, domain spoofing, temporary DNS issues, IP reputation problems, modifications to SPF records, and shared IP environments where the behavior of other users affects authentication. Google Postmaster Tools also considers alignment, similar to DMARC, meaning that SPF success isn't solely about passing the check, but also aligning with the 'Mail From' domain.
Key opinions
- Misconfiguration: Incorrect SPF record syntax, exceeding DNS lookup limits, or failing to include all authorized sending IPs are common causes of SPF failures.
- Third-Party Senders: Using CRMs, ESPs or other third-party email services without properly configuring SPF to authorize their sending servers leads to authentication dips.
- DNS Issues: Temporary DNS resolution problems can cause intermittent SPF check failures, leading to short-term drops in authentication rates.
- IP Reputation: Low IP reputation impacts SPF results, particularly on shared IPs where the behavior of other senders on the same IP address affects authentication.
- SPF Alignment: Google Postmaster Tools considers SPF alignment, meaning SPF success requires alignment with the 'Mail From' domain, and discrepancies between DKIM signing domain and SPF domain.
Key considerations
- Monitor SPF Records: Continuously monitor SPF records for unintended changes, errors, or the need for updates to include new sending sources.
- Authorize All Sending Sources: Ensure all sending sources, including third-party services and CRMs, are properly authorized in the SPF record.
- SPF Flattening: Consider 'flattening' SPF records to avoid exceeding DNS lookup limits, especially when using multiple 'include:' mechanisms.
- Address DNS Issues: Investigate and resolve temporary DNS resolution problems that may cause intermittent SPF failures.
- Monitor IP Reputation: Monitor your IP reputation and take steps to improve it if necessary, especially when using shared IPs.
Marketer view
Email marketer from Email Geeks explains that the Google Postmaster Tools authentication dashboard considers alignment, like DMARC, and that dips to 0% on SPF may be due to domain spoofing or unauthenticated sends. Insufficient send volume might also prevent data points from displaying, holding the line at its previous value.
5 May 2025 - Email Geeks
Marketer view
Email marketer from Reddit explains that if using a CRM, SPF should be configured to include the CRM's sending servers. Dips in SPF authentication could mean the CRM's IP addresses aren't consistently included in the SPF record, or the CRM is using different IPs.
23 Jan 2025 - Reddit
What the experts say
2 expert opinions
SPF authentication dips in Google Postmaster Tools graphs are primarily caused by two main factors: the use of third-party senders or ESPs without proper SPF configuration, and misconfiguration of SPF records combined with negative IP reputation. These issues directly impact email deliverability, leading to potential authentication failures and sender reputation damage.
Key opinions
- Third-Party Senders: Failure to include the sending source's IP addresses or domain (via 'include:') in the SPF record when using third-party senders or ESPs will result in authentication failures.
- Misconfiguration & Reputation: Misconfiguration of SPF records combined with a negative IP reputation, especially on shared IPs, contributes significantly to SPF authentication dips and negatively impacts sender reputation.
- Impact on Deliverability: Authentication errors will have a negative impact on the sender reputation, impacting deliverability of future emails.
Key considerations
- SPF Record Accuracy: Ensure that SPF records are correctly configured to include all authorized sending sources, including third-party senders and ESPs.
- Monitor IP Reputation: Actively monitor IP reputation, especially if using shared IPs, and take steps to maintain or improve it to avoid negative impacts on SPF authentication.
- Review sender processes: Regularly review sender processes to identify any misconfigurations that would impact Authentication.
Expert view
Expert from Spam Resource explains that SPF authentication dips directly impact email deliverability. These dips often are a result of misconfiguration of records and the negative reputation of shared IPs. Temporary and sustained Authentication errors will always have a negative impact on your sender reputation.
27 Sep 2024 - Spam Resource
Expert view
Expert from Word to the Wise explains that SPF failures, leading to dips in Postmaster Tools graphs, often occur when using third-party senders or ESPs. If the SPF record does not include the sending source's IP addresses or domain via 'include:', authentication will fail.
17 Sep 2022 - Word to the Wise
What the documentation says
4 technical articles
Based on the documentation, dips in SPF authentication rates within Google Postmaster Tools indicate underlying issues with SPF configuration, unauthorized sending sources, or syntax errors in SPF records. While DMARC may still pass due to DKIM, SPF failures, including both hard and soft fails, can impact reputation and contribute to these dips.
Key findings
- Configuration Issues: Dips in SPF rates often point to SPF configuration problems, such as failing to authorize legitimate sending sources.
- SPF Fail Types: SPF failures can be hard (rejection) or soft (suspicious), and Google Postmaster Tools may distinguish between them in reporting.
- Impact Despite DMARC: SPF failures can negatively affect reputation even if a DMARC policy is in place and passes due to DKIM alignment.
- Syntax Errors: Even minor syntax errors or typos in the SPF record can cause complete authentication failure and contribute to dips.
Key considerations
- Review SPF Configuration: Regularly review and audit SPF configurations to ensure all authorized sending sources are included and properly configured.
- Monitor for Syntax Errors: Carefully check SPF records for syntax errors, as even small mistakes can invalidate the entire record.
- Address Sending Sources: Address unauthorized sending sources to protect your domain from spoofing and improve authentication rates.
- Test SPF Records: Regularly test that your SPF records are working as expected by using testing tools.
Technical article
Documentation from Microsoft Learn explains that SPF failures can be either hard fails or soft fails. A hard fail indicates the email should be rejected, while a soft fail suggests the email is suspicious. Google Postmaster Tools may treat these differently, leading to dips.
25 Aug 2024 - Microsoft Learn
Technical article
Documentation from RFC 7208 (the SPF standard) explains that syntax errors in the SPF record can cause authentication failures. Even minor typos can invalidate the entire SPF record, resulting in authentication dips.
14 Aug 2022 - RFC Editor
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