Why do emails get blocked by Gmail for authentication despite correct SPF and DKIM DNS records?
Matthew Whittaker
Co-founder & CTO, Suped
Published 25 May 2025
Updated 18 Aug 2025
7 min read
It's a frustrating scenario: you've diligently set up your Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) records, double-checked them, and yet your emails are still getting blocked by Gmail for authentication failures. The bounce message explicitly states something like "550-5.7.26 Your email has been blocked because the sender is unauthenticated. Gmail requires all senders to authenticate with either SPF or DKIM. Authentication results: DKIM = did not pass SPF = did not pass."
This can be incredibly confusing, especially when you're certain your DNS records are correct. If SPF and DKIM are indeed set up, why would Gmail still report them as failing? This usually points to a more nuanced issue beyond a simple missing record. Often, the problem lies in the implementation, the sending process, or other factors influencing how Gmail evaluates your emails.
Let's explore the common reasons why your emails might still be blocked by Gmail for authentication, even when your SPF and DKIM DNS records appear to be correctly configured on the surface.
One of the most frequent culprits is that the sending IP address or service is not actually authorized in your SPF record. Even if you have an SPF record, if the email isn't originating from a server listed within it, Gmail will see an SPF failure. This is common when using third-party email services, marketing platforms, or HR systems that send emails on your behalf.
Similarly, DKIM issues often stem from improper signing by the sending server. The DKIM signature added to your email headers must match the public key published in your DKIM TXT records. If any part of the email's header or body covered by the signature is altered in transit, or if the sending server isn't correctly applying the signature, DKIM authentication will fail. This can be particularly tricky to diagnose without examining the full email headers.
Another often-overlooked factor is the existence of multiple SPF records for a single domain. You should only ever have one SPF record. If you have more, mail servers may ignore them or interpret them incorrectly, leading to authentication failures. Additionally, the SPF record might exceed the 10-DNS-lookup limit, causing it to fail validation.
Common SPF & DKIM configuration issues
Multiple SPF records: Having more than one SPF record on your domain.
SPF lookup limit: Exceeding the 10 DNS lookup limit in your SPF record can cause a TempError.
Incorrect IP addresses or domains: Not including all valid sending IP addresses or domains in your SPF record.
DMARC and sender reputation
Even with seemingly correct SPF and DKIM records, DMARC (Domain-based Message Authentication, Reporting, and Conformance) plays a critical role. Gmail and Yahoo now require DMARC for senders, especially bulk senders, to ensure proper email authentication. If your DMARC record is not configured correctly, or if your SPF or DKIM fail to align with your DMARC policy, emails may be rejected or sent to spam.
DMARC alignment requires that the domain in your email's "From" header (the one users see) matches the domain that passed SPF or DKIM. If your SPF passes for a different domain than the MAIL FROM (or Return-Path) domain, or if your DKIM signature is for a subdomain that doesn't align with the From header domain, your emails will fail DMARC, leading to delivery issues.
Ultimately, your sender reputation plays a massive role. Even with perfect authentication, a poor sender reputation can lead to emails being blocked or routed to the spam folder. High spam complaints, sending to invalid or old email addresses (which can turn into spam traps), or sudden spikes in sending volume can all negatively impact your reputation with Gmail and Yahoo. Gmail uses these signals, among others, to determine inbox placement, regardless of authentication status.
To troubleshoot authentication failures, start by obtaining the full bounce message. This message often contains specific error codes and details about which authentication check failed (SPF, DKIM, or DMARC), and why. For example, a 550-5.7.26 error from Gmail explicitly states unauthenticated sender.
Example Gmail Bounce Message
550-5.7.26 Your email has been blocked because the sender is unauthenticated.550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM.550-5.7.26 550-5.7.26 Authentication results:550-5.7.26 DKIM = did not pass550-5.7.26 SPF [spcbrasil.com.br]= did not pass
Next, use a reliable email deliverability test. These tools can simulate sending an email and provide a detailed report on your SPF, DKIM, and DMARC configuration, including any alignment issues or DNS lookup problems. They can highlight subtle errors that might not be immediately obvious in your DNS records.
Regular monitoring of your DMARC reports is also essential. DMARC reports provide granular data on how your emails are performing regarding authentication, showing you which emails pass or fail SPF and DKIM, and where they are failing. This feedback loop is crucial for identifying and resolving persistent authentication issues, helping you protect your domain from spoofing and ensuring legitimate emails reach the inbox.
Maintaining deliverability
Before troubleshooting
Manual checks: Verify your SPF and DKIM DNS records manually. Look for typos, extra spaces, or missing quotes.
Email service provider: Confirm your email service provider (ESP) is correctly applying DKIM signatures.
Ongoing monitoring and maintenance are crucial for sustained email deliverability. DNS records can sometimes be altered inadvertently, or new sending services might be introduced without proper SPF and DKIM updates. Regularly checking your domain's authentication status and reviewing your DMARC reports will help you catch issues early. It's also important to maintain a healthy sending reputation by keeping your email lists clean and sending relevant content.
For specific "DKIM = did not pass" or "SPF = did not pass" errors, it's often a DNS resolution issue or a problem with how the email is being handled by an intermediary. Sometimes, issues can be transient, like temporary DNS failures. Sending a test email and checking its headers or using a deliverability test tool can help verify if the problem persists or was a momentary glitch. If you're using a third-party sending service like Infobip, confirm with them if there have been any issues with their IP ranges. Further troubleshooting steps are available here.
Also, ensure that your SPF record is using the correct mechanism for your sender. For example, if you're sending from Google Workspace, your SPF record should include include:_spf.google.com. A common mistake is to miss these crucial includes or IP addresses, leading to authentication failures even when the record syntax is otherwise correct.
Views from the trenches
Best practices
Always use DMARC with a reporting policy (p=none) from the start.
Monitor DMARC aggregate reports daily to catch authentication failures early.
Ensure SPF records include all legitimate sending IPs and `include` mechanisms.
Verify DKIM signatures are properly applied by your email service provider.
Maintain clean email lists to reduce bounces and spam complaints.
Common pitfalls
Having multiple SPF records for the same domain, which invalidates them.
Exceeding the 10-DNS-lookup limit in your SPF record, leading to soft failures.
Not aligning the 'From' header domain with SPF or DKIM domains for DMARC.
Assuming correct DNS setup means emails are authenticated, ignoring DMARC reports.
Forgetting to update SPF/DKIM when switching or adding new email senders.
Expert tips
Use an online SPF lookup tool to confirm the record resolves correctly and isn't too long.
Check the raw email headers of a blocked email for detailed SPF, DKIM, and DMARC results.
Implement a DMARC policy with 'p=none' initially to gather reports without affecting delivery.
Consult your ESP's documentation for their recommended SPF and DKIM configurations.
Monitor your domain's reputation using Google Postmaster Tools if you send to Gmail users.
Expert view
Expert from Email Geeks says that if you have issues with SPF, you might have to check your DNS for broken records. Sometimes it's a transient DNS failure.
2024-04-01 - Email Geeks
Marketer view
Marketer from Email Geeks says that you need to be transparent and share the full, un-redacted bounce messages for an accurate diagnosis of authentication issues.
2024-04-02 - Email Geeks
Key takeaways for reliable email delivery
Encountering email blocks from Gmail despite seemingly correct SPF and DKIM records can be frustrating. However, the solution often lies in looking beyond the surface-level DNS setup.
By understanding the nuances of SPF and DKIM implementation, paying close attention to DMARC alignment, and proactively monitoring your sender reputation, you can significantly improve your email deliverability. Remember, email authentication is a dynamic process that requires ongoing vigilance and proper configuration across all your sending sources. Regular checks and attention to detail will help ensure your emails reach their intended recipients without unnecessary blocks or trips to the spam folder.
Gmail for authentication, even when your SPF and DKIM DNS records appear to be correctly configured on the surface.
Infobip, confirm with them if there have been any issues with their IP ranges. Further troubleshooting steps are available here.
