What causes email authentication failures when using Klaviyo DKIM and SPF, and how can I identify the root cause?

Key findings

• Misconfiguration: Incorrect setup of SPF records, DKIM keys, or DMARC policies is a leading cause of authentication failures, leading to messages being flagged as spam.
• Forwarding issues: Email forwarding can break DKIM signatures or SPF alignment, as the message headers are altered, leading to authentication failures even if the initial setup was correct.
• Security gateways: Security Email Gateways (SEGs) can modify email content, insert banners, or rewrite links, inadvertently breaking existing SPF and DKIM authentication.
• Domain alignment: Proper domain alignment between the From: address and the authenticated domains (SPF and DKIM) is critical for DMARC pass rates, as highlighted by Klaviyo's documentation. If there's a mismatch, DMARC will fail.
• Unrecognized sending sources: Seeing Klaviyo DKIM selectors or SPF domains in DMARC reports from unrecognized IPs can indicate unauthorized sending or complex routing issues, rather than penetration testing.

Key considerations

• Review DMARC reports: These reports provide granular data on SPF, DKIM, and DMARC authentication results, helping identify the exact sources of failures. Learn more about why DMARC authentication fails.
• Check email headers: Analyzing the full email headers provides a detailed breakdown of authentication checks (SPF, DKIM, DMARC) and their results for each hop.
• Verify SPF records: Ensure your SPF record includes all legitimate sending sources for your domain, including Klaviyo's includes, and doesn't exceed the 10-lookup limit.
• Validate DKIM setup: Confirm that your DKIM record is correctly published in your DNS and that the DKIM signature is not being invalidated by intermediary systems. A simple guide to DMARC, SPF, and DKIM can help.
• Investigate unusual IPs: If DMARC reports show failures from IPs you don't recognize but still use your domain's authentication, investigate if it's due to forwarding or a compromised account rather than generic penetration testing.

Key opinions

• Unauthenticated sources: Many email failures are simply due to unauthenticated email sources, which could be anything from compromised machines to generic spam or unexpected forwarding.
• Confusion over reports: Marketers often see Klaviyo DKIM and SPF domains in DMARC reports that they don't recognize, leading to confusion about whether it's legitimate activity or a security threat. They sometimes mistake these for penetration testing.
• Importance of authentication: There's a strong consensus that proper authentication (SPF, DKIM, DMARC) is non-negotiable for proving email legitimacy and avoiding the spam folder, as highlighted by industry advice.
• Recipient mailbox reporting: It's a common observation that the recipient mailbox might report the security gateway as the sending source, especially if it's the last hop before delivery, which can complicate troubleshooting.

Key considerations

• Verify authentication setup: Marketers must regularly check that their SPF, DKIM, and DMARC records are correctly configured to prove legitimacy and improve deliverability. Our guide on Klaviyo DMARC, SPF, and DKIM setup issues can help.
• Identify root causes: Instead of ignoring suspicious DMARC reports, marketers should investigate them to identify the true root cause, whether it's forwarding issues or potential unauthorized use.
• Check domain and DKIM selectors: When troubleshooting, always confirm if the From: address and DKIM signature match what your normal mail uses, as this often indicates forwarding issues.
• Proactive troubleshooting: Regularly auditing your email deliverability, including authentication checks, is crucial for maintaining good sender reputation and inbox placement. Our expert guide on why your emails fail provides further insight.

Key opinions

• Intermediary modifications: Experts commonly point out that Security Email Gateways (SEGs) often modify email messages by inserting banners, rewriting links, or adding tracking pixels, which can inadvertently break DKIM signatures and lead to authentication failures.
• Forwarding is problematic: Email forwarding is frequently cited as a major cause of authentication failures, as the forwarding server can alter the email in a way that invalidates the original DKIM signature or SPF check.
• DMARC's role: DMARC acts as a crucial reputation guard, preventing unauthorized sources from sending on your behalf and relying on SPF and DKIM alignment to determine legitimacy.
• Alignment issues: Many DMARC failures, even with seemingly correct SPF and DKIM, are caused by alignment issues where the From: domain doesn't align with the domains authenticated by SPF or DKIM.
• Beyond obvious spam: For messages not flagged as overt spam, experts often find that a significant number are either missing SPF, failing SPF, or failing DKIM.

Key considerations

• Analyze the full email path: To troubleshoot effectively, experts recommend examining the entire email delivery path, paying close attention to any intermediary servers or security gateways that might be altering the message. This also helps when boosting email deliverability rates.
• Understand DMARC alignment: Even with correct SPF and DKIM records, DMARC can fail if the domains used in authentication don't align with the From: header. This is a subtle but critical point.
• Beware of SPF DNS timeouts: Some environments, like Microsoft, can experience SPF DNS timeouts if the record is too complex or involves too many lookups, leading to intermittent failures. Our guide explains why your emails fail at Microsoft.
• Monitor DMARC reports closely: Use DMARC aggregate and forensic reports to gain a comprehensive view of authentication results, even for forwarded or modified messages. This helps pinpoint exactly where failures occur.
• Consider security gateway impact: If a recipient uses a security gateway, be aware that it might modify your emails, which could break DKIM signatures. This is a common, often overlooked, cause of failures.

Key findings

• DMARC compliance: Many warnings or failures, particularly for personal inboxes, are direct results of DMARC failing, emphasizing the necessity of being DMARC compliant.
• Domain alignment: A critical point for deliverability is ensuring domain alignment, where the sender's email address domain matches the root domain of the sending infrastructure, such as Klaviyo's. This is explicitly stated in Klaviyo's official deliverability documentation.
• Common DKIM failure reasons: Incorrect DKIM record syntax, DKIM alignment issues, and neglecting DKIM for third-party senders are frequently listed as primary causes of DKIM failures.
• SPF record lookups: Documentation warns that an SPF record with too many lookups (exceeding the 10-lookup limit) can lead to authentication failures.

Key considerations

• Check DMARC for compliance: Regularly verify your DMARC setup to ensure compliance and avoid emails being rejected or quarantined. Issues can lead to emails going to spam.
• Verify email headers: As a primary diagnostic step, documentation advises viewing email headers to check the specific SPF, DKIM, and DMARC authentication results.
• Ensure correct DKIM syntax: Pay close attention to the syntax of your DKIM records. Even minor errors can cause failures. This is a common pitfall noted in technical guides.
• Monitor DMARC reports: Utilize DMARC reports to understand where and why authentication is failing, enabling targeted fixes. Comprehensive guides on troubleshooting DMARC reports provide useful insights.