Summary
It can be perplexing when your carefully configured SPF and DKIM records occasionally result in authentication failures. While the expectation might be a clear pass or fail for every email, real-world email delivery is more nuanced. This can occur even with large volumes of email, leading to a small percentage of messages failing authentication despite everything appearing to be correctly set up. These intermittent failures often stem from factors outside the sender's direct control, such as email forwarding, specific recipient server behaviors, or transient network issues.
Key findings
- Partial failures: SPF and DKIM authentication can show small percentages of failures even during large sends where the majority of emails pass, rather than a definitive 0% or 100% success rate.
- Email forwarding: A common cause for SPF and DKIM failures is email forwarding, where the message passes through an intermediary server that alters the email, breaking the original authentication.
- DKIM design intent: DKIM was not designed to achieve a 100% success rate, and occasional failures are anticipated by its creators.
- DMARC tolerance: A low DMARC failure rate, such as 0.1%, is often considered normal and is not typically a cause for concern.
Key considerations
- Investigate forwarding: If you observe intermittent SPF or DKIM failures, consider whether email forwarding or third-party services are involved. Learn how to identify forwarders.
- Analyze DMARC reports: DMARC aggregate reports provide visibility into authentication failures, including SPF and DKIM, and can help pinpoint the source of issues, especially when considering DMARC reports from Google and Yahoo.
- Focus on DMARC alignment: While individual SPF or DKIM failures can occur, the primary goal is often DMARC alignment. If DMARC passes, minor SPF or DKIM failures might be acceptable. This is especially relevant when DMARC authentication fails despite SPF and DKIM passing.
- Review third-party services: Sending through ESPs or other services that modify email headers or bodies can impact SPF and DKIM. Ensure your setup accounts for these third-party behaviors.
What email marketers say
Email marketers often encounter situations where SPF and DKIM results are not consistently 100% successful, even when their records appear to be correctly configured. This can be confusing, particularly when working with deliverability testing tools that report a small percentage of authentication failures across a large email send. The primary concern for marketers is ensuring messages reach the inbox, and partial failures can introduce uncertainty.
Key opinions
- Confusion over partial failures: Marketers find it counterintuitive for SPF and DKIM to exhibit anything other than a 0% or 100% failure rate, expecting a binary pass/fail given their sending environment and signature setup.
- Unexpected outcomes: It's surprising for a single email send with many deliveries to result in some SPF failures while others succeed.
- DMARC passing despite SPF/DKIM issues: Some third-party services might consistently fail SPF alignment, but if DKIM passes, DMARC checks can still succeed, making isolated SPF failures less critical.
Key considerations
- Interpreting reports: It's crucial for marketers to understand how their testing tools report SPF and DKIM authentication to accurately interpret partial failures. Consider using our email deliverability tester for comprehensive analysis.
- Troubleshooting methodology: When facing intermittent failures, check email headers for authentication results to pinpoint the exact cause, especially for Gmail SPF/DKIM issues.
- Contextual understanding: Small failure rates (e.g., 0.1% for DMARC) are often considered normal and may not warrant immediate alarm if overall deliverability remains strong, especially when considering the insights from the HubSpot Community.
Marketer view
Email marketer from Email Geeks observes that they received a report indicating SPF and DKIM failures via Glock Apps, and they are trying to understand the data. The report suggests a small number of SPF and DKIM failures compared to the total number of deliveries, which is confusing given their expectation of either 0% or 100% success.
Marketer view
Email marketer from Latenode Official Community indicates that SPF alignment issues in DMARC, despite emails being delivered, often stem from email forwarding or the use of third-party services that alter the envelope sender. They note that services like Gmail might sometimes contribute to this behavior.
What the experts say
Email deliverability experts recognize that SPF and DKIM authentication are not always perfect, even with optimal configurations. They attribute intermittent failures to various factors, including the fundamental design of these protocols and the complex nature of email routing. Experts often emphasize that a small percentage of failures is statistically normal and not necessarily indicative of a misconfiguration.
Key opinions
- Forwarding breaks authentication: Email forwarding is a significant cause of SPF and DKIM failures because the message's path changes, causing the authentication to break at the forwarding step.
- DKIM's inherent variability: DKIM was not designed for 100% success; it can randomly fail due to reasons such as issues with key retrieval from DNS or body modifications during transit.
- Normal DMARC failure rates: A DMARC failure rate of around 0.1% is considered normal and is commonly observed by deliverability experts across their client bases.
- Loss of control post-send: Once an email leaves the sender's system, control over its journey is lost, and various factors can cause authentication to fail at later stages.
Key considerations
- Diagnose forwarding impact: Experts recommend understanding the email forwarding chain (sender -> first recipient -> final destination) to identify points where SPF and DKIM might fail. This is crucial for troubleshooting DKIM failures across various ISPs.
- Accept minor failures: Do not overreact to very low percentages of authentication failures. Focus on the overall DMARC pass rate rather than isolated SPF or DKIM issues if they are minimal.
- Advanced troubleshooting: When issues persist, delve into the details of your email environment and configurations. For instance, investigate hidden SPF DNS timeouts that can affect Microsoft.
- Continuous monitoring: Regular DMARC reporting and analysis are key to identifying patterns in authentication failures and understanding their impact over time.
Expert view
Expert from Email Geeks explains that SPF and DKIM authentication protocols frequently break during the forwarding process. This occurs when an email is initially sent to a recipient, who then forwards the message, rule, or distribution list, leading the final destination to check the authentication based on the forwarding server rather than the original sender.
Expert view
Expert from WordtotheWise indicates that SPF failures can occur when the receiving server attempts too many DNS lookups while validating the SPF record. This can exceed the 10-lookup limit, causing a PermError (permanent error) and SPF validation failure.
What the documentation says
Official documentation and technical guides shed light on the intricacies of SPF and DKIM, explaining why these authentication mechanisms might not always achieve perfect pass rates. These resources often detail the specifications that govern how SPF and DKIM work, including their vulnerabilities to common email routing practices like forwarding and message modification. They also clarify the expected behavior of these protocols, emphasizing that transient errors and certain configurations can lead to intermittent failures.
Key findings
- Email authentication issues: DMARC failures often occur due to problems with email authentication, domain alignment, or incorrect configurations of SPF and DKIM.
- SPF permanent errors: A 'permanent error' in SPF indicates that the SPF record could not be correctly processed, leading to message delivery failure, often due to syntax issues or exceeding lookup limits.
- DKIM signature validity: DKIM signatures become invalid if the signature domain and sender domain do not match or if the email body is modified after signing.
- DMARC deployment challenges: Initial DMARC deployment can fail due to mistakes in the DMARC record itself, causing DMARC checks to be unsuccessful.
Key considerations
- Understand DMARC failures: Documentation emphasizes that DMARC failures can stem from authentication, alignment, or configuration issues. Delve into what a DMARC failure is to diagnose these problems.
- Proper configuration is key: Ensure your authentication protocols, especially DKIM, are correctly configured to minimize failures. This includes avoiding typos and using the right selectors, as outlined in our guide on DKIM selector name examples.
- Monitor DNS propagation: Be aware of DNS propagation delays, as these can cause intermittent DKIM failures even if the record is technically correct.
- Address DMARC record mistakes: Review your DMARC record carefully for errors that could cause checks to fail. Our free DMARC record generator tool can help prevent common errors.
Technical article
Documentation from Certera's blog explains that a DMARC failure can stem from several reasons, including problems with email authentication, incorrect domain alignment, or errors in configuration settings. These issues directly impact the success of SPF and DKIM.
Technical article
Documentation from TechTarget defines a 'permanent error' in SPF as an instance where the SPF record cannot be correctly processed, leading to the message being undelivered. This type of error can occur due to various issues within the SPF record's structure or the DNS lookup process.
Related resources
12 resources
Related pages
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