Summary
Troubleshooting DKIM failures requires a multi-faceted approach focusing on DNS configuration, selector matching, and content integrity. Begin by verifying the DKIM record setup, ensuring accurate syntax, key length, and selector alignment in both the DNS and email headers. Validate the public key's validity using tools like xnnd.com and online DKIM checkers (Mailhardener, MXToolbox). Address content alterations during transit by testing various forwarding scenarios and examining raw email headers; consider implementing ARC. Employ a hierarchy of checks, sending test emails to multiple providers (Gmail, Hotmail, Yahoo), and analyzing results. Prioritize strong key generation, regular key rotation, and DMARC implementation for monitoring and policy enforcement. Tools like `dig`, nslookup, Google Admin Toolbox's Messageheader, Microsoft's Test-DkimSignature cmdlet, and dmarcian's DKIM Inspector aid in diagnosis. While Gmail is often seen as a standard, it's crucial to recognize that no single mailbox provider is a perfect reference implementation.
Key findings
- DNS Configuration: Incorrect DNS records, syntax errors, key length issues, and selector mismatches are primary causes of DKIM failures.
- Content Alteration: Email content modification during transit, often by forwarding services or email clients adding disclaimers, invalidates the DKIM signature.
- Selector Matching: The DKIM selector used in the email header must precisely match the selector specified in the DNS record.
- Tool Dependency: Diagnosing DKIM failures relies heavily on specialized tools for DNS lookup, DKIM signature validation, and header analysis.
- Provider Variance: DKIM validation behavior varies among email providers, requiring testing with multiple providers.
Key considerations
- DNS Auditing: Regularly audit DNS records and DKIM configurations to ensure accuracy and prevent misconfigurations.
- Key Management: Implement strong DKIM keys and rotate them regularly to enhance security.
- ARC Implementation: Consider implementing ARC to preserve authentication results when emails are forwarded.
- DMARC Enforcement: Implement DMARC policies to monitor and enforce email authentication and receive failure reports.
- Forwarding Tests: Rigorously test email sending through various forwarding scenarios to identify issues with content modification.
What email marketers say
8 marketer opinions
Troubleshooting DKIM failures involves several key steps: verifying DNS record syntax and correctness, ensuring the DKIM selector matches in both the email header and DNS, and checking for content alteration during email transit, which can be caused by forwarding or email clients adding disclaimers. Tools like online DKIM checkers (Mailhardener, MXToolbox), DNS lookup tools (`nslookup`), and analyzing raw email headers are essential for diagnosing issues. Implementing strong DKIM keys, rotating them regularly, and using DMARC for monitoring and enforcement are also critical preventive measures. Testing with multiple email providers (Gmail, Yahoo, Hotmail) helps identify provider-specific issues.
Key opinions
- DNS Configuration: Incorrect DNS record syntax, incorrect key length, or using multiple DKIM records are common errors.
- Selector Mismatch: A mismatch between the DKIM selector in the email header and DNS record causes validation failures.
- Content Alteration: Email content modification during transit (e.g., by forwarding or disclaimers) invalidates the DKIM signature.
- Tool Usage: Online DKIM checkers, DNS lookup tools, and raw email header analysis are crucial for diagnosis.
- Provider Variance: DKIM validation can vary across different email providers (Gmail, Yahoo, Hotmail).
Key considerations
- Regular Audits: Regularly audit DKIM configurations and DNS records for accuracy and proper setup.
- Key Management: Generate strong DKIM keys and rotate them regularly for enhanced security.
- DMARC Implementation: Implement DMARC to monitor and enforce email authentication policies and receive reports on DKIM failures.
- Testing: Send test emails through various forwarding scenarios to check for content alterations.
- Content Signing Practices: Implement proper content signing practices to minimize unintended alterations.
Marketer view
Email marketer from MXToolbox shares that they offer a DKIM record lookup tool and a DKIM authentication test, which can be used to check the validity of the DKIM record and the signature of a sample email, to assist with troubleshooting.
5 Jun 2024 - MXToolbox
Marketer view
Email marketer from SparkPost explains that a common reason for DKIM invalidity is alteration of the email content between signing and delivery, which can be caused by forwarding services or email clients adding footers or disclaimers. They advise implementing proper content signing practices and regularly monitoring DKIM results.
7 Jan 2025 - SparkPost
What the experts say
5 expert opinions
Troubleshooting DKIM failures involves a structured approach. It begins with verifying the public key's validity using tools like xnnd.com. Next, running an authentication test with kbxscore.com helps identify broader issues. Testing by sending emails to Gmail and Hotmail is crucial, noting Gmail's leniency and Microsoft's sensitivity to DNS problems. Incorrect DNS records, selector mismatches between the email header and DNS, and content alteration by forwarding services are common causes. Tools like `dig` are helpful for DNS diagnosis. Consider using ARC to preserve authentication results. While Gmail is a practical standard, no provider is perfect.
Key opinions
- DNS Issues: Incorrect DNS records are a frequent cause of DKIM failures; syntax and publication must be checked.
- Selector Mismatch: Mismatched DKIM selectors in the email header and DNS record lead to validation errors.
- Content Alteration: Forwarding services can modify email content, invalidating the DKIM signature.
- Provider Sensitivity: Different email providers (Gmail, Hotmail) have varying levels of sensitivity to DKIM and DNS issues.
- Gmail as Standard: Gmail is a practical, though not perfect, standard for DKIM implementation due to its large user base.
Key considerations
- Public Key Validation: Always verify the public key's validity to identify intermittent failures.
- Authentication Tests: Use authentication testing tools to ensure your DKIM setup passes the required checks.
- Forwarding Tests: Send test emails through forwarding scenarios to evaluate DKIM pass/fail results.
- ARC Implementation: Consider using ARC to maintain authentication results even when emails are forwarded.
- Tools Utilization: Leverage tools like `dig` and online DKIM checkers to diagnose DNS and signature issues.
Expert view
Expert from Word to the Wise explains that forwarding services can sometimes alter email content, invalidating the DKIM signature. To troubleshoot, send test emails through various forwarding scenarios and examine the headers for DKIM pass/fail results. Consider using ARC (Authenticated Received Chain) to preserve authentication results through forwarding.
22 Feb 2025 - Word to the Wise
Expert view
Expert from Email Geeks shares a hierarchy of checks for troubleshooting DKIM failures: 1. Check the public key's validity using tools like xnnd.com to look for intermittent failures. 2. Run an auth test using tools like kbxscore.com to see if everything passes. 3. Check via sending to Gmail and Hotmail accounts, noting that Gmail is forgiving while Microsoft is more sensitive to DNS issues. Microsoft may also have DKIM failures due to encoding issues.
24 Dec 2023 - Email Geeks
What the documentation says
3 technical articles
Troubleshooting DKIM failures, as outlined by Google, Microsoft, and dmarcian, centers on verifying DNS configuration, ensuring DKIM selectors match, and checking for content modifications during transit. Google recommends its Messageheader tool, Microsoft advises using message trace logs and the Test-DkimSignature cmdlet in PowerShell, and dmarcian suggests its DKIM Inspector and DMARC monitoring services. Common root causes include incorrect DNS settings, content alteration during forwarding, and signing server issues.
Key findings
- DNS Configuration: Incorrect DNS configuration is a primary cause of DKIM failures.
- Selector Mismatch: The DKIM selector used must match the selector in the DNS record.
- Content Modification: Alterations to email content during transit, such as by forwarding services, can invalidate DKIM.
- Signing Server Issues: Problems with the email signing server can lead to DKIM failures.
Key considerations
- DNS Verification: Regularly verify that the DKIM record is correctly configured in DNS settings.
- Tool Utilization: Use available tools (Google Messageheader, Microsoft PowerShell cmdlets, dmarcian DKIM Inspector) to diagnose DKIM issues.
- Monitoring: Implement DMARC monitoring to track DKIM performance and identify failures.
Technical article
Documentation from dmarcian explains that DKIM failures often stem from incorrect DNS configuration, modifications to the email body during transit (such as by a forwarding service), or issues with the signing server. They recommend using their DKIM Inspector tool and DMARC monitoring services to identify and resolve these issues.
22 Feb 2024 - dmarcian
Technical article
Documentation from Google Workspace Admin Help explains that to troubleshoot DKIM failures, administrators should verify that the DKIM record is properly configured in the DNS settings, ensure the selector used in the DKIM record matches the selector used when signing the email, and check for any modifications to the email content during transit that could invalidate the DKIM signature. Tools like Google Admin Toolbox's Messageheader tool can assist in analyzing email headers for DKIM status.
20 May 2025 - Google Workspace Admin Help
