What causes SPF authentication dips in Google Postmaster Tools graphs?
Matthew Whittaker
Co-founder & CTO, Suped
Published 4 Jun 2025
Updated 17 Aug 2025
8 min read
Seeing dips in your SPF authentication graphs within Google Postmaster Tools can be confusing, especially when other authentication methods like DKIM and DMARC remain consistently high. Many senders experience these fluctuations and wonder if they signify a critical issue or simply a peculiarity of how Google reports data. It's a common concern that can leave you scratching your head, trying to pinpoint the exact cause of a sudden drop.
I've often seen situations where SPF authentication rates briefly drop to 0% for a day or so before returning to 100%, or exhibit smaller, more prolonged dips. Understanding these dips requires looking beyond just whether SPF passed or failed; it often involves grasping how Google Postmaster Tools interprets email authentication and the nuances of SPF itself.
SPF (Sender Policy Framework) is an email authentication protocol that helps prevent email spoofing. It allows a domain owner to specify which mail servers are authorized to send email on their domain's behalf through a DNS TXT record. When a receiving mail server gets an email, it checks the SPF record of the sending domain to verify that the email originated from an authorized server. If the sender's IP address is listed in the SPF record, it passes authentication. If not, it can be marked as failed.
In Google Postmaster Tools, the SPF graph specifically shows the percentage of mail that passed SPF authentication versus all mail from that domain that attempted SPF, as outlined by Mailjet in their deliverability blog. It's important to differentiate between an SPF record simply validating the sending IP and SPF alignment. SPF alignment, crucial for DMARC, means that the domain in the Return-Path (envelope sender) domain matches the From: header domain or its organizational domain. Google Postmaster Tools, however, primarily reports on the SPF pass rate, not necessarily alignment. This distinction can sometimes lead to confusion when comparing with DMARC reports, which factor in alignment.
A common point of confusion arises when emails are sent through a third-party CRM or Email Service Provider (ESP). These services often handle the SPF authentication using their own domains in the Return-Path while still allowing you to send from your domain in the From: header. In such cases, your domain's SPF record may not be the one undergoing the actual SPF check, leading to a 0% SPF pass rate in Postmaster Tools for your domain, even if the emails are successfully delivered because DKIM or DMARC are passing. This is why you might see SPF authentication rates fluctuate in your graphs.
Several factors can cause those unexpected SPF authentication dips, even when you believe everything is correctly configured. One common culprit is sending email from IP addresses that are not included in your SPF record. If you introduce a new email sending service, an internal mail server, or even a marketing automation platform without updating your SPF record, those emails will likely fail SPF checks, leading to a drop in your reported authentication rates.
Another factor is exceeding the 10 DNS lookup limit for SPF records. Each include, a, mx, and ptr mechanism in your SPF record counts as a DNS lookup. If your record requires more than 10 lookups, receiving servers will often return a PermError, causing SPF authentication to fail. This is a common issue for organizations using multiple third-party senders.
Temporary DNS issues, such as an unreachable DNS server or a transient network problem, can also cause SPF authentication dips. While typically short-lived, these can result in temporary failures. Additionally, if you're experiencing a sudden spike in email bounce rates, especially from Gmail, it could sometimes be related to SPF issues leading to emails being rejected outright rather than just failing authentication silently.
DNS lookup limit: An SPF record exceeding 10 DNS lookups results in a permanent error.
Syntax errors: Incorrectly formatted SPF records can lead to validation failures.
Third-party senders: ESPs often use their own Return-Path domains, causing your domain's SPF to show 0%.
Diagnosing and troubleshooting dips
The most effective way to diagnose SPF dips is to cross-reference your Google Postmaster Tools data with DMARC reports. While Postmaster Tools offers a general overview, DMARC reports provide granular detail, showing SPF pass/fail rates, alignment issues, and the specific sending IPs involved. This can help confirm if the dip is due to misconfigurations, unauthorized sending, or expected behavior from your ESP.
If you notice a dip, the first step is to review your SPF record for any recent changes or errors. Check for common issues like typos, missing IP addresses, or the aforementioned 10 DNS lookup limit. You might also need to investigate if any new services or departments have started sending email on your behalf without proper SPF inclusion. For a detailed troubleshooting guide, refer to resources on demystifying SPF TempError in DMARC reports.
Also, consider the volume of email sent on days when dips occur. Google Postmaster Tools requires a sufficient volume of emails to display data points accurately. If your sending volume is very low on a particular day, the graph might show an artificial dip or simply no data, maintaining the last reported line until more data becomes available. Always look for corroborating evidence in your DMARC reports before assuming a critical issue.
Scenario: SPF dip, DKIM/DMARC remain 100%
Cause: Often occurs when sending through an ESP that uses its own domain for SPF (in the Return-Path) while your domain handles DKIM.
Scenario: All authentication (SPF, DKIM, DMARC) dips
Cause: Indicates unauthorized sending, spoofing, or a widespread misconfiguration impacting all protocols.
Impact: Potentially severe deliverability issues, including emails going to spam or being rejected. Requires immediate investigation.
When to worry about SPF authentication dips
The good news is that not every SPF dip in Google Postmaster Tools indicates a catastrophic problem. As mentioned, if you're using a CRM or ESP that handles the Return-Path for SPF, then your domain's SPF record showing 0% or low authentication in Postmaster Tools is actually expected. In these scenarios, your emails are typically still authenticated via DKIM and DMARC, ensuring good deliverability. This is why it's crucial to look at the other authentication graphs in Postmaster Tools as well, particularly DKIM and DMARC.
The primary concern arises when your DKIM or DMARC authentication rates also drop, or if you know your SPF record should be handling authentication for your primary sending streams and it's consistently low. A brief, single-day dip often points to a transient network issue or a very low sending volume for that specific day, which may not be cause for alarm. However, consistent dips or sustained low SPF rates when your domain should be authenticating via SPF warrant a deeper investigation into your DNS settings and sending practices.
Ensure all legitimate sending sources are included in your SPF record to avoid authentication failures.
Regularly review your SPF record for syntax errors and to prevent exceeding the 10 DNS lookup limit.
Set up DMARC monitoring to gain deeper insights into authentication results and identify specific failure reasons.
Common pitfalls
Forgetting to update SPF records when adding new email sending services or changing providers.
Ignoring SPF PermErrors (too many DNS lookups) which invalidate your record.
Not cross-referencing Postmaster Tools data with DMARC reports for a complete picture.
Expert tips
Investigate SPF dips alongside DKIM and DMARC graphs for a comprehensive understanding.
Low email volume can cause Postmaster Tools graphs to appear erratic or show no data.
Ensure your DNS records are stable and accessible to avoid transient authentication failures.
Expert view
Expert from Email Geeks says that the Google Postmaster Tools authentication dashboard also looks for alignment, similar to DMARC, not just whether SPF passes.
2023-10-25 - Email Geeks
Expert view
Expert from Email Geeks notes that if there's insufficient send volume for a day, Gmail might not display a data point, causing the graph line to remain stagnant until new data appears.
2023-10-25 - Email Geeks
Ensuring stable email authentication
SPF authentication dips in Google Postmaster Tools graphs can be alarming, but they aren't always indicative of a severe problem. Often, they stem from nuances in how third-party sending services handle SPF, or from transient issues like low sending volume. The key is to understand the context of the dip and to look at the broader picture of your email authentication.
By regularly monitoring your DMARC reports and ensuring your SPF records are correctly configured for all your sending domains, you can gain much-needed clarity. Remember that consistent high rates in DKIM and DMARC often mitigate the impact of SPF dips, ensuring your emails continue to land in the inbox. For further help, explore our resources on Google Postmaster Tools to improve your email deliverability.
Proactive monitoring and a thorough understanding of authentication protocols are your best defense against deliverability issues. Don't let occasional dips mislead you; focus on maintaining strong overall email authentication practices.
