Summary
When authenticated emails to Gmail soft bounce with DKIM and SPF fail errors, it indicates a critical issue with how your sending domain is perceived and validated by Gmail's servers. Despite seemingly correct setup, these errors suggest that Gmail either cannot find, validate, or align your SPF and DKIM records with the sending domain and IP address. Such a situation can lead to significant deliverability problems, as Gmail prioritizes authenticated mail to protect its users from spam and phishing. Understanding the nuances of these authentication protocols and how Gmail interprets them is crucial for troubleshooting.
Key findings
- Gmail's strict authentication policy: The error message 550-5.7.26 explicitly states that mail is unauthenticated and has been blocked due to security risks. This underscores Gmail's heightened focus on authentication, requiring at least SPF or DKIM to pass.
- Authentication not recognized: Even if SPF and DKIM are properly authenticated on your end, Gmail's rejection means it's not validating them correctly. This could be due to issues with record publication, DNS resolution, or alignment.
- Multiple authentication failures: The bounce message indicates both DKIM and SPF checks failed, suggesting a fundamental problem with the authentication setup for the sending domain or IP address.
- DNS issues are common: Problems with DNS hosting or recent DNS migrations can prevent SPF and DKIM records from being properly resolved by recipient servers, even if they are present.
Key considerations
- Verify record publication: Confirm that your SPF and DKIM records are correctly published in your domain's DNS and are discoverable by external queries. Tools can help double-check if things are indeed in shape.
- Review authentication implementation: Examine how your sending system is applying SPF and DKIM signatures. An incorrect configuration, even if the records exist, can lead to failures.
- Check email headers: Analyze the email headers of bounced messages sent to Gmail. This will provide specific details on why SPF and DKIM checks failed, offering clearer diagnostic information. Our email deliverability tester can help with this.
- Consult official guidelines: Refer to Gmail's official authentication guidelines for detailed instructions on setting up authentication. This is the primary resource Google recommends for troubleshooting these errors.
What email marketers say
Email marketers often face challenges with authentication despite believing their setup is correct. When Gmail rejects emails with SPF and DKIM failures, it triggers a scramble to understand why the authentication isn't being recognized. Many marketers focus on the immediate interpretation of the bounce message, which clearly states a failure in authentication, leading them to re-verify their DNS records and sending practices. The consensus is to trust the bounce message and diligently investigate potential discrepancies between the intended setup and Gmail's validation.
Key opinions
- Trust the bounce message: If Gmail's bounce message explicitly states SPF and DKIM failures, it's generally accurate. Marketers are advised to believe the error message and focus on diagnosing the authentication setup rather than external factors initially.
- Re-check authentication: Even if authentication appears to be set up, the first step should be to thoroughly re-examine the SPF and DKIM records for any misconfigurations or omissions.
- Verify sender domain: Ensure the From address and domain are properly aligned with the authenticated domain, as this is a common source of DMARC-related issues which build on SPF and DKIM.
- Potential DNS or server issues: Consider the possibility of underlying DNS hosting problems, recent migrations, or issues with the sending server itself that might be preventing Gmail from successfully validating the records.
Key considerations
- Utilize diagnostic tools: Use online tools to check the validity and propagation of your SPF and DKIM records to ensure they are accessible and correctly formatted. This can provide immediate feedback on any publishing errors.
- Review DMARC implications: While the bounce specifies SPF/DKIM, DMARC relies on their alignment. A failure in these can lead to DMARC alignment failures, increasing the likelihood of bounces or spam placement.
- Check email sending practices: Ensure that the email service provider (ESP) or sending platform is correctly signing emails with DKIM and that the SPF record includes all IP addresses or domains used for sending. This is a common pitfall leading to emails going to spam.
- Submit a bulk sender escalation: If confident that your setup is flawless, Google offers a form to submit samples for reconsideration by their team.
Marketer view
Marketer from Email Geeks suggests that if you're experiencing soft bounces with SPF and DKIM fail errors, the error message itself is the most reliable indicator. They advise trusting what Google explicitly states in its bounce notifications, as these messages are usually precise in identifying the type of authentication failure.Therefore, the initial focus should be on verifying that the email's authentication, including SPF and DKIM, is correctly set up and being recognized by Google's servers. This often involves a detailed review of DNS records and the sending infrastructure to ensure everything aligns with Google's requirements.
Marketer view
Marketer from SendLayer highlights that recent Google updates prioritize authenticated emails, meaning unauthenticated messages are increasingly rejected. They emphasize that proper SPF and DKIM records are no longer optional but a necessity for successful email delivery.To fix soft bounces and prevent email blocking, marketers must ensure these authentication methods are correctly implemented and actively verifying their sending domain. This preventative measure is key to maintaining a good sending reputation and inbox placement.
What the experts say
Experts in email deliverability emphasize that when Gmail reports SPF and DKIM failures, it's a strong indication of a misconfiguration on the sender's side, rather than an error by Gmail itself. They highlight the importance of thoroughly investigating DNS records, sending server configurations, and the proper alignment of domains within authentication standards. The core message is to trust Google's bounce feedback and systematically eliminate potential issues, focusing on the correct publication and validation of authentication records to restore deliverability.
Key opinions
- Google's word is law: Experts strongly advise that if Google's bounce message indicates a problem, it's accurate. They suggest that the issue almost certainly lies with the sender's authentication setup.
- Records might be missing: The phrasing of the bounce message, especially 'did not pass', implies that SPF and DKIM might not even be present or correctly applied in the message headers for Gmail to authenticate against.
- DNS hosting reliability: Inconsistent or spotty DNS host platforms can lead to issues where authentication records aren't reliably available for lookup by recipient servers like Gmail. Recent DNS migrations are also a common culprit for missing records.
- Key must be published: A DKIM signature is useless if the corresponding public key is not published in the DNS. Gmail cannot verify the signature without access to this key.
Key considerations
- Thorough DNS audit: Conduct a comprehensive audit of your DNS records to ensure SPF and DKIM are correctly configured and propagated across all relevant DNS servers. Consider using a DMARC record generator for accuracy.
- Examine message headers: Obtain the full email headers from a bounced message sent to Gmail. These headers provide crucial forensic data that pinpoints the exact failure point for SPF and DKIM. This is part of a broader strategy for troubleshooting DMARC failures.
- Confirm sending IP inclusion: For SPF, ensure that the IP address of the sending server is explicitly listed in your SPF record, either directly or via an include mechanism.
- DMARC alignment: While the immediate error is SPF/DKIM, DMARC requires alignment between the From domain and the SPF/DKIM authenticated domains. Failures here can cause further problems, necessitating understanding DMARC reports.
Expert view
Expert from Email Geeks explains that if Google provides a bounce message indicating an authentication failure, it is highly likely that the issue originates from the sender's configuration. They assert that Google's error messages are typically precise and should be taken at face value.This means that the problem is not with Google, but rather with how the sender's domain or IP address is failing to properly authenticate against SPF and DKIM checks, requiring a thorough review of the sender's setup.
Expert view
Expert from SpamResource.com suggests that SPF failures can often stem from an SPF record that is either missing the correct sending IPs or has too many lookups, leading to a DNS lookup limit error. They explain that SPF records must be meticulously crafted to include all authorized sending sources.Failure to include every legitimate sending IP or domain in the SPF record will result in SPF failing for those specific sends, causing Gmail to reject the unauthenticated mail.
What the documentation says
Official documentation from email providers and standardization bodies (like Google and RFCs) provides the definitive guidelines for email authentication. When authenticated emails to Gmail soft bounce with DKIM and SPF fail errors, the documentation outlines the precise requirements for these protocols. It clarifies that both SPF and DKIM must be correctly configured in DNS, with proper alignment to the sending domain, to ensure successful validation by receiving mail servers. Any deviation from these standards, even minor, can lead to authentication failures and subsequent deliverability issues.
Key findings
- Authentication is mandatory for Gmail: Gmail documentation clearly states that emails must be authenticated with SPF or DKIM. Failure to do so results in messages being rejected or marked as spam.
- SPF validation: SPF verifies the sender's IP address against a list of authorized sending IPs published in the domain's DNS. If the sending IP is not authorized, SPF fails.
- DKIM validation: DKIM uses a cryptographic signature embedded in the email header, verifiable by a public key published in DNS. If the signature doesn't match the key, or the key is unavailable, DKIM fails.
- DMARC reinforces SPF/DKIM: While not explicitly in the error, DMARC builds upon SPF and DKIM by requiring alignment between the From domain and the authenticated domains. A DMARC policy can instruct receivers to block or quarantine emails that fail SPF or DKIM and their alignment checks.
Key considerations
- Correct DNS record syntax: Ensure that your SPF (TXT record) and DKIM (TXT record) are syntactically correct and follow the specified format. Even minor errors can render them invalid.
- Include all sending sources in SPF: Your SPF record must list all authorized IP addresses and domains that send email on behalf of your domain. Missing entries will cause SPF failures for those sources.
- Proper DKIM key publishing: The public DKIM key must be correctly published in your DNS under the specific selector name used by your sending system. If the key is not accessible or incorrect, DKIM will fail.
- Monitor DMARC reports: Regularly review DMARC aggregate and forensic reports to identify consistent SPF or DKIM failures. These reports provide detailed insights into where and why authentication is failing, helping you to fix common DMARC issues.
Technical article
Documentation from Google Postmaster Tools states that a high percentage of unauthenticated email will negatively impact your sender reputation and deliverability to Gmail users. It explicitly outlines the requirements for SPF and DKIM to pass authentication checks.This means that for consistent inbox delivery, all emails must be properly authenticated. Any soft bounces with SPF/DKIM fail messages indicate a direct violation of these guidelines, prompting immediate corrective action on the sender's part.
Technical article
RFC 7208 (SPF) outlines that an SPF record defines which IP addresses are authorized to send email on behalf of a domain. It specifies that if an email originates from an IP not listed in the SPF record, it should result in a soft fail or hard fail, depending on the record's policy.Therefore, if Gmail reports an SPF failure, it means the sending IP was not recognized as legitimate by your published SPF record. This necessitates updating the record to include all valid sending sources to ensure proper authentication.
Related resources
12 resources
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