Summary
Fluctuations in SPF authentication within Google Postmaster Tools arise from a multitude of factors, including improper SPF alignment, misconfigured or outdated SPF records (missing sending sources, syntax errors, and failure to include regional endpoints), email forwarding issues, inconsistent sending practices (bulk sends failing SPF, shared IP reputation impacts, and variable sending volumes), temporary DNS errors, and exceeding SPF record lookup limits. Accurate SPF record maintenance, adherence to SPF alignment, and implementation of solutions like SRS for forwarding are crucial for achieving consistent SPF authentication.
Key findings
- SPF Alignment: Inconsistencies in SPF alignment (MAIL FROM domain vs. authentication domain) lead to fluctuations.
- Record Configuration: Misconfigured SPF records (missing sources, unauthorized third parties) and syntax errors trigger failures.
- Outdated Records: Outdated or incomplete SPF records cause SPF authentication to fail.
- Email Forwarding: Email forwarding breaks SPF due to IP mismatches unless SRS is in place.
- Inconsistent Sending: Inconsistent practices like bulk sends failing SPF or variable sending volumes impact authentication.
- Shared IP Impact: Shared IP addresses can cause fluctuations due to varying sender reputations.
- DNS Errors: Temporary DNS errors can intermittently cause SPF checks to fail.
- Lookup Limits: Exceeding SPF record lookup limits results in authentication failures.
- Regional Endpoint: Missing AWS regional endpoints in SPF records can impact SPF.
Key considerations
- Record Accuracy: Regularly check and update SPF records to include all authorized sending sources and valid syntax.
- SPF Alignment: Ensure the 'MAIL FROM' domain matches the authenticating domain.
- Forwarding Solution: Implement SRS or similar mechanisms if email forwarding is common.
- DMARC Reports: Utilize DMARC reports to identify SPF failure sources and implement corrective measures.
- IP Reputation: Monitor and maintain sending IP reputation, especially on shared IPs.
- DNS Stability: Ensure stable DNS infrastructure to prevent temporary errors.
- 3rd Party Senders: Manage third-party senders meticulously, updating SPF records with IP changes.
- Regional Endpoints: Include relevant regional endpoints in SPF records for AWS or similar services.
- Sending Practice: Maintain consistent sending practices to ensure stable results
What email marketers say
12 marketer opinions
Fluctuations in SPF authentication within Google Postmaster Tools can stem from various factors related to email sending practices, SPF record configuration, and network conditions. Key causes include inconsistent sending volumes, bulk sends failing SPF, shared IP reputation, email forwarding, temporary DNS errors, exceeding SPF record lookup limits, and improperly configured third-party senders. Ensuring accurate SPF record maintenance, proper alignment, and implementing solutions like SRS for forwarding are critical for stable SPF authentication.
Key opinions
- Inconsistent Sending: Fluctuations often occur due to inconsistent sending volumes or bulk sends that fail SPF checks.
- Shared IP Issues: Using a shared IP address can lead to SPF fluctuations due to the varying reputation of other senders on the same IP.
- Forwarding Impact: Email forwarding frequently breaks SPF authentication because the sending server no longer matches the original sender's IP, unless SRS is implemented.
- DNS Errors: Temporary DNS errors can cause SPF checks to intermittently fail.
- Lookup Limits: Exceeding the SPF record lookup limit (10 DNS lookups) can result in SPF failures.
- Third-Party Senders: Using third-party senders without properly including their IPs in the SPF record will lead to SPF failures.
- Domain Alignment: Ensuring proper SPF alignment (matching the 'MAIL FROM' domain with the authenticating domain) is essential for consistent SPF results.
Key considerations
- SPF Record Accuracy: Regularly check and update your SPF record to ensure all authorized sending sources are included and that there are no syntax errors.
- Subdomain Use: Consider using a subdomain for marketing emails to isolate the impact of other email streams on your top-level domain.
- DMARC Monitoring: Utilize DMARC reports to identify sources of SPF failures and take corrective actions.
- SRS Implementation: If email forwarding is common, implement Sender Rewriting Scheme (SRS) to preserve SPF authentication.
- IP Reputation: Monitor and maintain your sending IP reputation, especially when using shared IPs.
- DNS Stability: Ensure your DNS infrastructure is stable to avoid temporary errors that can affect SPF checks.
- Third-Party Management: Maintain a clear list of all third-party senders and their IP addresses, and regularly update your SPF record to reflect any changes.
- Consistent Sending Practices: Try to keep the volume of email consistent.
Marketer view
Email marketer from Reddit shares that using a shared IP address can cause SPF fluctuations because the reputation of other senders on the same IP can impact your SPF results. Another user also stated that inconsistent sending volumes may also affect the reputation score.
10 Feb 2025 - Reddit
Marketer view
Email marketer from Mailjet.com shares that regularly checking your SPF record for accuracy is crucial. Using SPF record checker tools can help identify and correct any errors that may be causing intermittent failures.
25 Jul 2021 - Mailjet.com
What the experts say
3 expert opinions
Fluctuations in SPF authentication, as reported in Google Postmaster Tools, are primarily caused by issues related to SPF record configuration and email sending practices. These include: having email sources not listed in the SPF record, inconsistent sending practices like using different IPs or services without updating the record, and email forwarding, which often breaks SPF due to IP address mismatches. To address these fluctuations, ensuring accurate and up-to-date SPF records, properly managing sending sources, and implementing mechanisms like SRS for email forwarding are crucial.
Key opinions
- Missing Email Sources: At least one of the email sources is not included in the SPF record, causing authentication failures.
- Inconsistent Sending Practices: Using different sending IPs or services without updating the SPF record leads to SPF fluctuations.
- Email Forwarding Issues: Email forwarding causes SPF to fail because the original sender's IP no longer matches the sending server.
Key considerations
- Update SPF Records: Ensure all authorized sending sources are accurately listed in the SPF record and that the record is kept up-to-date.
- Manage Sending Sources: Maintain consistent sending practices, using only authorized sending IPs and services.
- Implement SRS for Forwarding: If email forwarding is common, implement Sender Rewriting Scheme (SRS) or similar mechanisms to maintain SPF authentication.
Expert view
Expert from Word to the Wise shares that email forwarding often causes SPF to fail because the original sender's IP no longer matches the sending server. If forwarding is common for your emails, it's critical to implement Sender Rewriting Scheme (SRS) or similar mechanisms to maintain SPF authentication.
30 Oct 2022 - Word to the Wise
Expert view
Expert from Email Geeks explains that at least one of the email sources is not in the SPF record and this is unrelated to DMARC (although DMARC reports will be able to tell you which sources of email are failing SPF and why the DKIM signature is passing but DMARC is failing).
30 Aug 2023 - Email Geeks
What the documentation says
5 technical articles
Fluctuations in SPF authentication within Google Postmaster Tools can be attributed to inconsistencies in SPF alignment, improperly configured SPF records, syntax errors within the SPF record, outdated or incomplete SPF records, and the failure to include relevant regional endpoints (particularly when using services like AWS). Ensuring proper alignment, accurate configuration, and regular updates of the SPF record, alongside syntax validation, are crucial for maintaining consistent SPF authentication results.
Key findings
- SPF Alignment Issues: Inconsistencies in SPF alignment, where the 'MAIL FROM' domain doesn't match the authenticating domain, can cause fluctuations.
- Improper SPF Configuration: DMARC failures linked to SPF arise from SPF records not configured to encompass all sending sources or unauthorized third-party senders.
- Syntax Errors: Syntax errors in the SPF record can lead to intermittent authentication failures.
- Outdated SPF Records: Maintaining an up-to-date SPF record with all current sending sources is critical; outdated records lead to failures.
- Missing Regional Endpoints: When utilizing services like AWS, failure to include relevant regional endpoints in the SPF record results in inconsistent authentication.
Key considerations
- Ensure SPF Alignment: Verify that the domain used in the 'MAIL FROM' address matches the authenticating domain.
- Configure SPF Correctly: Accurately configure the SPF record to include all sending sources and authorized third-party senders.
- Validate SPF Syntax: Regularly check the SPF record for syntax errors to prevent intermittent failures.
- Update SPF Records Regularly: Keep the SPF record up-to-date with all current sending sources.
- Include Regional Endpoints: When using services like AWS, ensure that the regional endpoints are included in the SPF record.
Technical article
Documentation from DMARC.org explains that DMARC failures related to SPF can be caused by a number of reasons, including the SPF record not being properly configured to include all sending sources, or the use of third-party senders who are not authorized in the SPF record.
8 Jan 2022 - DMARC.org
Technical article
Documentation from RFC Editor specifies that syntax errors in the SPF record can cause the SPF check to fail. These errors can lead to inconsistent authentication results if they are intermittently triggered.
19 May 2023 - RFC Editor
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