Summary
DKIM signature failures in Microsoft Office 365 are a multifaceted issue stemming from various sources, encompassing interoperability problems, DNS configuration errors, key management inadequacies, and procedural oversights. A potential lack of interoperability between Microsoft's DKIM implementation and older versions of OpenDKIM can lead to verification failures. Incorrect DNS settings, particularly after migration, are a common pitfall. The use of inadequate DKIM key sizes (below 2048 bits), coupled with a lack of regular key rotation, compromises security. Furthermore, mail flow configurations involving third-party security gateways, email forwarding practices, and DMARC misalignment can all contribute to these failures. Transport rules modifying emails and the presence of invalid or missing DKIM DNS records are also significant factors. Troubleshooting involves meticulous DNS record verification, proper key management, ensuring DMARC alignment, monitoring DKIM reports, and adhering to established DKIM standards.
Key findings
- OpenDKIM Incompatibility: An incompatibility exists between Microsoft's DKIM implementation and older versions of OpenDKIM.
- DNS Errors: Incorrect DNS configuration, especially post-migration, is a common cause.
- Small Key Size: Use of DKIM keys smaller than 2048 bits affects deliverability.
- Gateway Interference: Third-party security gateways can disrupt DKIM signatures.
- Forwarding Issues: Email forwarding often invalidates DKIM signatures.
- DMARC Misalignment: DKIM misalignment within a DMARC policy impacts email authentication.
- Transport Rule Modification: Transport rules modifying email content can break DKIM.
- 1024 bit key usage: Use of 1024 bit keys invalidates DKIM signatures.
Key considerations
- Update OpenDKIM: Update OpenDKIM to the latest version.
- Verify DNS: Double-check MX, SPF, and DKIM records post-migration.
- Stronger Keys: Upgrade DKIM keys to 2048 bits.
- Gateway Config: Configure security gateways to pass DKIM signatures.
- Implement SPF/DMARC: Implement SPF and DMARC for enhanced authentication.
- DMARC Monitoring: Monitor DMARC reports for insights.
- Review Transport: Review transport rules for alterations.
- Check for invalid characters: Look for invalid DNS record issues and special characters
- Follow DKIM best practices: Regularly rotate DKIM keys, use a strong key length (2048 bits recommended), and monitor your domain's reputation.
What email marketers say
11 marketer opinions
DKIM signature failures in Microsoft Office 365 can stem from a variety of issues, including incorrect DNS settings after migration, mail flow configurations with third-party security gateways, improper key management, email forwarding modifications, and DMARC alignment problems. Monitoring DKIM reports and addressing DNS record errors are crucial for resolving these failures. Incorrect transport rules, the use of 1024 bit keys and ensuring key rotation are also vital.
Key opinions
- Migration Issues: Incorrect DNS settings following a migration to Office 365 are a frequent cause of DKIM failures.
- Third-Party Gateways: Mail flow configurations involving third-party email security gateways can interfere with DKIM signatures.
- Key Management: Improper DKIM key management practices, including lack of rotation and monitoring, can compromise email authentication.
- Email Forwarding: Email forwarding can modify email content, leading to DKIM verification failures.
- DMARC Alignment: Lack of DKIM alignment as part of a DMARC policy can negatively impact email deliverability.
- Obsolete Key Length: Use of 1024 bit keys invalidates DKIM signatures.
Key considerations
- DNS Verification: Carefully review and verify MX, SPF, and DKIM records after any migration or configuration change.
- Gateway Configuration: Ensure that any third-party email security gateways are correctly configured to pass DKIM signatures unmodified.
- Key Rotation: Implement a plan for regularly auditing and rotating DKIM keys to maintain security.
- DMARC Implementation: Implement SPF and DMARC policies in addition to DKIM to enhance email authentication and deliverability.
- DMARC Monitoring: Monitor DMARC reports to identify sources of DKIM failure and authentication issues.
- Transport Rules: Review and configure Transport Rules to prevent modification of emails.
- Key Upgrade: If using 1024 bit keys, upgrade to 2048 bit keys.
Marketer view
Email marketer from ProofPoint explains that monitoring a domain using DMARC reports provide insight into DKIM failures and authentication issues. He suggests using DMARC reports to identify the sources of DKIM failure, and then work to resolve these failures at the source.
16 Jul 2023 - ProofPoint
Marketer view
Email marketer from Mailjet advises that proper DKIM key management is essential for maintaining email authentication. They suggest regularly auditing your DKIM keys, monitoring for any signs of compromise, and having a plan in place for quickly rotating keys if necessary.
23 May 2023 - Mailjet
What the experts say
6 expert opinions
DKIM signature failures in Microsoft Office 365 can be attributed to a few core reasons. There's a potential interoperability issue between Microsoft's DKIM implementation and OpenDKIM, leading to verification failures. DNS configuration errors, especially after migration, are another common culprit. Finally, using outdated DKIM key sizes (less than 2048 bits) can also cause deliverability problems. Updating OpenDKIM, correctly configuring DNS records, and upgrading to larger key sizes are recommended solutions.
Key opinions
- OpenDKIM Incompatibility: An interoperability issue exists between Microsoft's DKIM and older versions of OpenDKIM.
- DNS Configuration Errors: Incorrect DNS settings post-migration to Microsoft 365 are a frequent cause of DKIM failures.
- Outdated Key Sizes: Using DKIM keys smaller than 2048 bits can lead to deliverability problems.
Key considerations
- Update OpenDKIM: Consider updating OpenDKIM to the latest version to address potential interoperability issues.
- Verify DNS Records: Carefully double-check DNS TXT records after migrating to Microsoft 365 to ensure they are correctly configured with the right selector, domain, and public key.
- Upgrade Key Size: Upgrade DKIM keys to 2048 bits to align with current security best practices and improve deliverability.
Expert view
Expert from Word to the Wise explains that DKIM failures often occur after migrating to Microsoft 365 due to DNS configuration errors. Double-check that your TXT record is set up correctly. The selector value, the domain, and the public key value must match what Microsoft has provided.
2 Jul 2023 - Word to the Wise
Expert view
Expert from Email Geeks suspects that updating to the latest version of OpenDKIM would fix the algorithm incompatibility issue.
27 Apr 2023 - Email Geeks
What the documentation says
6 technical articles
DKIM signature failures in Microsoft Office 365 arise from several root causes, primarily related to DNS configuration, key management, and adherence to DKIM standards. Improper DNS record configuration, including errors in syntax, key values, and selector settings, frequently leads to failures. DNS propagation delays can also temporarily cause issues. Maintaining a strong key length (2048 bits is recommended) and regularly rotating DKIM keys are essential for security. It's vital to ensure implementations correctly handle header fields and signature algorithms according to the DKIM standard. Troubleshooting includes verifying the DKIM selector, confirming the public key matches the private key, validating signature format, and monitoring domain reputation.
Key findings
- DNS Configuration Errors: Common DKIM record errors include syntax errors, incorrect key values, and special characters in the DNS record.
- DNS Propagation Delays: DNS propagation delays can temporarily cause DKIM failures.
- Key Size Limitations: Inadequate DKIM key lengths (less than 2048 bits) impact security and may cause deliverability issues.
- Algorithm Handling: Incorrect handling of header fields and signature algorithms as per the DKIM standard results in verification failures.
- Key Rotation Practices: Lack of regular DKIM key rotation compromises security.
Key considerations
- Verify DNS Records: Double-check DNS records for syntax errors, incorrect key values, and special characters.
- Ensure DNS Propagation: Allow sufficient time for DNS changes to propagate fully.
- Use Strong Key Lengths: Utilize a DKIM key length of at least 2048 bits for stronger security.
- Adhere to DKIM Standard: Ensure implementations correctly handle header fields and signature algorithms as outlined in the DKIM standard (RFC 6376).
- Regularly Rotate Keys: Implement a policy for regularly rotating DKIM keys to maintain security and prevent compromise.
- Test Email: Retrying sending a new test email can resolve DKIM signature failures.
Technical article
Documentation from Google explains that if a DKIM signature fails, it can be because of DNS issues, problems with the signing process, or invalid characters. It suggests that you check and make sure that the DNS record is valid, and to retry sending a new test email. If the issue persists, you may have to regenerate the DNS record.
13 Mar 2022 - Google Workspace Admin Help
Technical article
Documentation from RFC Editor specifies that the DKIM standard requires implementations to correctly handle various header fields and signature algorithms. The standard outlines potential reasons for signature verification failures, and provides guidance for robust DKIM implementation.
24 Dec 2023 - RFC Editor
Can email signatures, especially via Exclaimer, cause SPF or DKIM failures and impact email delivery?
Does UCE Protect Level 3 at an ESP affect delivery to major ISPs like Hotmail or Office 365?
Does UCEPROTECTL3 listing impact email deliverability, especially with Microsoft Office 365?
How can I improve email deliverability with Microsoft and avoid spam filters?
How do I fix DKIM alignment errors and configure DKIM signing for a custom domain in Microsoft 365 and is include:spf.mtasv.net required for mailchimp?
What actions should I take if my inbox is spoofed and how will it impact my sender reputation?
