What causes email authentication failures when using Klaviyo DKIM and SPF, and how can I identify the root cause?
Matthew Whittaker
Co-founder & CTO, Suped
Published 26 Jun 2025
Updated 17 Aug 2025
8 min read
Email authentication, specifically SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), is fundamental for ensuring your emails reach the inbox and avoid spam folders. When sending emails through a platform like Klaviyo, you rely on these protocols to verify your sending identity and build trust with recipient mail servers.
However, it's not uncommon to encounter authentication failures, leading to deliverability issues. Understanding the common causes of these failures and how to accurately identify their root cause is crucial for maintaining a strong sender reputation and ensuring your marketing and transactional emails consistently reach your audience.
Authentication failures in Klaviyo emails can stem from various sources, ranging from simple misconfigurations to complex interactions with recipient mail systems. A primary cause is often incorrect DNS record setup. Even a small typo or an extra space in your SPF or DKIM records can invalidate them. Klaviyo generally handles the setup of these records automatically for dedicated sending domains, but manual adjustments or conflicts with other services on your domain can lead to problems.
Another common issue arises when emails are modified in transit. Some email security gateways (SEGs) or forwarding services might alter the email header or body, which can break the DKIM signature. When a DKIM signature is broken, the receiving server can no longer verify the email's authenticity, leading to a DKIM failure. This is particularly problematic because it often happens outside your direct control, making it harder to diagnose without access to DMARC reports.
Poor sender reputation can also indirectly lead to authentication issues being flagged more aggressively, even if your records are technically correct. If your domain or IP address is on a blocklist (or blacklist), or has a history of high spam complaints, recipient servers might be more scrutinizing of your authentication. While not a direct cause of a record being invalid, it can amplify the impact of minor authentication discrepancies.
Common causes
Incorrect DNS records: Typos, missing records, or improper values for SPF and DKIM entries.
Email forwarding or modification: Intermediate servers altering the email, breaking the DKIM signature.
Overly broad SPF records: Exceeding the 10-lookup limit can cause SPF to fail.
Specific SPF and DKIM troubleshooting scenarios
SPF (Sender Policy Framework) issues usually revolve around the SPF record itself being misconfigured or incomplete. Every domain should have only one SPF record, and it must include all authorized sending sources, including Klaviyo's SPF mechanism. If you miss an authorized sender or include too many `include`lookups (exceeding the 10-lookup DNS limit), SPF checks can fail. Remember that even minor formatting errors in the SPF record can cause authentication to fail, as highlighted by Nudgify's guide.
DKIM (DomainKeys Identified Mail) failures often point to issues with the DKIM key or the email content itself. Klaviyo generates DKIM records for your sending domain, but if the public key isn't correctly published in your DNS, or if there's a mismatch between the signing domain and the 'From' domain, DKIM will fail. Furthermore, any modification to the email content or headers after DKIM signing but before it reaches the recipient mail server will cause the DKIM signature to break, leading to a failure. Duocircle details common DKIM failure reasons.
Another subtle but critical factor is DMARC (Domain-based Message Authentication, Reporting, & Conformance) alignment. Even if SPF and DKIM pass individually, DMARC requires that the domain in the SPF-authenticated domain and the DKIM-signed domain align with the 'From' header domain. Klaviyo handles this for its dedicated sending domains, but if you're using a different setup or an outdated configuration, this alignment can fail, causing the overall DMARC authentication to fail, even when SPF and DKIM technically pass.
SPF challenges
Too many lookups: Exceeding the 10 DNS lookup limit in your SPF record.
Missing includes: Not authorizing all sending IPs or third-party senders.
Syntax errors: Incorrect formatting in the TXT record.
DKIM challenges
Incorrect key: Public key not matching the private key used for signing.
Message modification: Headers or body changed after signing.
Selector issues: Incorrect DKIM selector in DNS or email header.
SPF solutions
Consolidate includes: Use a single SPF record and manage authorized senders carefully.
Verify syntax: Use a SPF record checker to catch errors.
Check all sources: Ensure all services sending mail on your behalf are included.
DKIM solutions
DNS verification: Confirm the DKIM TXT record is published correctly.
Minimize modifications: Reduce email changes by intermediate systems.
Check alignment: Ensure the 'From' domain matches the DKIM signing domain.
Diagnosing authentication problems
The first step in identifying the root cause of an authentication failure is to analyze the email headers. Every email carries hidden headers that contain critical information about its journey and authentication results. Look for Authentication-Results headers, which will show you the pass/fail status for SPF, DKIM, and DMARC. This is often the quickest way to pinpoint which protocol is failing. Major inbox providers like Google and Outlook provide tools to view these headers easily. For a Gmail example, Klaviyo's help center explains how to view message originals.
Example email header showing authentication failuresplain
Authentication-Results: mx.google.com;
dkim=fail header.i=@yourdomain.com header.s=klaviyo header.b=...;
spf=fail (google.com: domain of bouncing-email@yourdomain.com does not designate X.X.X.X as permitted sender) smtp.mailfrom=bouncing-email@yourdomain.com;
dmarc=fail (p=quarantine sp=quarantine dis=quarantine) header.from=yourdomain.com
DMARC (Domain-based Message Authentication, Reporting, & Conformance) reports are another invaluable tool. These XML reports, sent to the email address specified in your DMARC record, provide an aggregated overview of your email streams, showing which emails are passing or failing SPF and DKIM, and why. By analyzing these reports, you can identify unauthorized sending sources, pinpoint configuration errors, and understand how various email receivers (like Google and Yahoo) are handling your mail. This data is essential for troubleshooting DMARC failures.
Sometimes, the issue isn't with your setup, but with how an intermediate server or recipient's security system handles your email. As previously mentioned, some security gateways (SEGs) will rewrite URLs or add disclaimers, which can invalidate DKIM signatures. If you notice authentication failures primarily with emails sent to specific domains or organizations, it's worth investigating if their security infrastructure is interfering with your email's authenticity. This often requires checking DKIM failures across different ISPs.
Authentication check
Result meaning
Common cause
SPF fail
The sending IP is not authorized in your SPF record.
Incorrect SPF record syntax, missing IP, or too many lookups.
DKIM fail
The email content or headers were modified after signing, or the signature is invalid.
DNS DKIM record incorrect, email modification by SEGs/forwarders.
DMARC fail
SPF and/or DKIM failed, or the aligned domain did not match the 'From' header.
SPF/DKIM failures, or DMARC alignment issues.
Advanced considerations for Klaviyo deliverability
When using Klaviyo, it's important to differentiate between shared and dedicated IP addresses. With a shared IP, your sender reputation is influenced by other users, which can sometimes impact deliverability if those users have poor sending practices. Dedicated IPs give you full control over your reputation, but also full responsibility. Klaviyo sets up authentication automatically for dedicated sending domains, which simplifies the process, but regular verification of your DNS records remains essential.
Forwarding can be a significant culprit for DKIM authentication failures. When an email is forwarded from one mailbox to another, the forwarding server often modifies the message's headers or body. This modification invalidates the original DKIM signature, leading to a DKIM fail at the final recipient's server. While you can't control how other servers forward mail, understanding this mechanism helps in interpreting DMARC reports, where you might see such failures attributed to the forwarding server's IP rather than your own sending infrastructure.
Finally, monitor your domain reputation closely. A low domain reputation, perhaps due to high spam complaint rates or presence on email blocklists (or blacklists), can cause ISPs to scrutinize your authentication more harshly, or even outright reject emails that might otherwise pass. Tools like Google Postmaster Tools, as mentioned by Klaviyo, can provide insights into your domain's health and help you proactively address potential deliverability issues before they lead to widespread authentication failures and spam placement.
Views from the trenches
Best practices
Routinely verify your SPF and DKIM records using online checkers to ensure correct syntax and publication.
Analyze DMARC reports regularly for insights into authentication outcomes and potential unauthorized senders.
Maintain a healthy sender reputation by monitoring engagement and minimizing spam complaints.
Ensure your 'From' domain aligns with your SPF and DKIM domains for successful DMARC pass rates.
Understand how email security gateways and forwarding services might impact your authentication.
Common pitfalls
Ignoring DMARC reports, missing critical insights into email authentication failures.
Having multiple SPF records or exceeding the 10 DNS lookup limit, causing SPF validation issues.
Failing to update DKIM keys when they expire or are rotated, leading to signature invalidation.
Assuming all authentication failures are malicious penetration tests when they could be legitimate forwarding.
Not considering the impact of intermediate email modifications on DKIM signatures.
Expert tips
Use a DMARC monitoring tool to easily interpret complex XML reports and quickly identify trends.
When troubleshooting, check the raw email headers first for immediate authentication pass/fail indicators.
Be aware that some recipient security gateways might alter emails, causing DKIM to break.
If emails are being forwarded, SPF and DKIM may legitimately fail due to message modification.
Always ensure your DMARC policy is robust enough to provide actionable data for investigation.
Expert view
Expert from Email Geeks says DMARC reports indicate that specific IP addresses are sending mail which may or may not be authorized.
March 15, 2024 - Email Geeks
Marketer view
Marketer from Email Geeks says those unauthenticated email sources could be compromised machines, email forwarding, or generic spam.
March 15, 2024 - Email Geeks
Ensuring robust email authentication
Email authentication failures, particularly with SPF and DKIM when using a platform like Klaviyo, can be frustrating and significantly impact your deliverability. However, by systematically approaching the problem, you can identify and resolve these issues. Key steps include meticulously checking your DNS records for accuracy, analyzing email headers for granular authentication results, and leveraging DMARC reports for a comprehensive overview of your email traffic.
Proactive monitoring and a deep understanding of how SPF, DKIM, and DMARC interact are essential. This approach not only helps in troubleshooting existing problems but also in preventing future authentication issues, ultimately safeguarding your sender reputation and maximizing your email campaign's reach.
Klaviyo, you rely on these protocols to verify your sending identity and build trust with recipient mail servers.
Google and Yahoo) are handling your mail. This data is essential for troubleshooting DMARC failures.
