Summary
Intermittent DKIM validation failures in Office 365 can be attributed to a multitude of factors ranging from DNS inconsistencies and misconfigurations to email body modifications and underlying infrastructure issues. Specifically, having differing DKIM keys across DNS servers, delays in DNS propagation, or incorrect DKIM signing settings within Office 365 are frequent causes. Furthermore, alterations to the email body during transit and issues with SPF/DMARC alignment can indirectly lead to DKIM failures. Problems with character encoding, outdated DNS setups, conflicting CNAME records, key rotation issues, and problematic server hops also contribute to this issue. Enabling DKIM may unearth pre-existing sending infrastructure problems. The DNS record should be audited for typos, and it is essential to investigate transit issues between hops.
Key findings
- DNS Configuration: DNS record inconsistencies, propagation delays, and multiple DNS servers with differing DKIM keys cause validation failures.
- Office 365 Settings: Incorrect DKIM signing policies within Office 365 lead to intermittent failures.
- Email Modification: Email content alteration during transit by middle servers corrupts DKIM signatures.
- SPF/DMARC: Misconfigured SPF and DMARC policies can indirectly cause DKIM failures.
- Encoding Issues: Character encoding problems within the email body corrupt DKIM signatures.
- Outdated DNS: Outdated DNS setups fail to update DKIM records automatically.
- CNAME Conflicts: Conflicting CNAME records for the same host cause DKIM validation problems.
- Key Rotation: Issues with key rotation necessitate verifying the current key's validity.
- Server Hops: Investigating server hops can identify problematic intermediaries.
- Infrastructure Issues: Enabling DKIM can reveal underlying problems within the email sending infrastructure.
- Human Error: Simple human errors such as typos in DNS records can be the main reason for failure.
Key considerations
- Synchronize DNS: Ensure DKIM records are consistent and fully propagated across all DNS servers.
- Verify O365 Settings: Double-check DKIM signing policies within Office 365 for correct domains and users.
- Audit Mail Flow: Investigate mail flow for content-altering intermediaries.
- Align SPF/DMARC: Ensure SPF and DMARC policies align with DKIM settings.
- Test Encoding: Regularly test emails for encoding-related problems.
- Automate DNS Updates: Implement automated DKIM DNS updates.
- Review CNAME Records: Verify no conflicting CNAME records exist.
- Maintain Keys: Regularly rotate and update DKIM keys.
- Track Server Hops: Implement tools to track and analyze server hops.
- Audit DNS Records: Ensure all DNS records are validated and error free.
- Address Underlying Issues: Evaluate sending infrastructure for pre-existing problems.
What email marketers say
7 marketer opinions
Intermittent DKIM validation failures with Office 365 can stem from various sources. DNS propagation delays or misconfigurations in SPF alignment, DMARC policies, or DNS settings can lead to DKIM failures. Email content issues like character encoding problems can corrupt signatures. Outdated DNS setups, conflicting CNAME records, key rotation issues, and problems in email server hops can also contribute to these intermittent failures.
Key opinions
- DNS Propagation: DNS propagation delays often cause intermittent DKIM issues, so verifying records with online tools is essential.
- SPF/DMARC: SPF alignment and DMARC policies can indirectly affect DKIM validation; misconfigurations can lead to failures.
- Character Encoding: Problems with character encoding in email content can corrupt DKIM signatures, causing validation failures.
- Outdated DNS: Old DNS setups might not automatically update DKIM records, requiring configuration verification.
- CNAME Conflicts: Other CNAME records for the same host can conflict and cause DKIM validation to fail.
- Key Rotation: Issues related to key rotation should be investigated by verifying that the key is up to date.
- Server Hops: Analyzing the email's server hops can help identify points of failure in DKIM validation.
Key considerations
- Monitor DNS: Continuously monitor DNS records for correct propagation and configuration to prevent intermittent issues.
- Review Policies: Regularly review SPF and DMARC policies to ensure they align with DKIM settings and prevent unexpected failures.
- Test Emails: Regularly test emails with different character sets and content to identify encoding-related problems.
- Automate DNS Updates: Ensure DNS updates for DKIM are automated to prevent issues from outdated records.
- Check CNAMEs: Verify that there are no conflicting CNAME records set for the same host as your DKIM record.
- Update Keys: Always ensure that DKIM keys are up-to-date and properly rotated to maintain email authentication.
- Analyse Server Hops: Implement tools to track and analyze server hops to identify any intermediaries causing DKIM validation failures.
Marketer view
Email marketer from StackExchange suggests that one way to find the issue is to investigate all the server hops that the mail passes through.
8 Nov 2021 - StackExchange
Marketer view
Email marketer from StackExchange responds that there could be issues relating to key rotation so you should verify the key is up to date.
23 Nov 2021 - StackExchange
What the experts say
5 expert opinions
Intermittent DKIM failures in Office 365 can stem from a combination of DNS issues, message modification in transit, and underlying sending infrastructure problems. DNS inconsistencies, such as having servers with different DKIM keys or general DNS propagation delays, are frequent culprits. Modifications to the email body during transit can invalidate the DKIM signature. Enabling DKIM can expose previously unnoticed issues within the sending setup. While the 'n' tag in a DKIM CNAME record isn't directly related to validation, DNS record problems such as typos or propagation issues are major contributors to DKIM problems.
Key opinions
- DNS Inconsistencies: Having multiple DNS servers with differing DKIM keys is a common cause of intermittent failures.
- Message Modification: Alterations to the email body during transit can invalidate the DKIM signature.
- Underlying Issues: Enabling DKIM can reveal pre-existing problems in sending practices or infrastructure.
- DNS Records: DNS Record issues and propagation problems are major contributors to DKIM problems.
- CNAME 'n' Tag: The 'n' tag in a DKIM CNAME record is for human-readable notes and does not affect validation.
Key considerations
- Check DNS Servers: Ensure all DNS servers have the same, valid DKIM key and that changes are fully propagated.
- Investigate Transit: Examine the email path for any intermediaries that might be modifying the message content.
- Review Infrastructure: Assess the sending infrastructure for underlying issues that DKIM might expose.
- Audit DNS Records: Audit and check your DNS records, ensure there are no typos and there are no propagation issues.
Expert view
Expert from Spam Resource explains that a very common cause of DKIM problems are DNS record problems. These include: not waiting long enough after the DNS change, typo's in the records or DNS servers having issues.
10 May 2024 - Spam Resource
Expert view
Expert from Email Geeks explains that the 'n' tag in a DKIM CNAME record is for human-readable notes and is not used in the validation process.
15 Sep 2024 - Email Geeks
What the documentation says
3 technical articles
According to Microsoft documentation, intermittent DKIM validation failures in Office 365 can arise from three primary issues: inconsistencies or delays in DNS record propagation, incorrect configuration of DKIM signing settings within Office 365, and alteration of email content during transit. Ensuring DNS records are fully propagated and consistent across servers, verifying the correct DKIM signing policy is enabled for the relevant domains and users, and investigating potential mail flow issues or third-party programs altering email content are crucial for resolving these failures.
Key findings
- DNS Issues: Inconsistent DNS records or propagation delays lead to intermittent DKIM failures.
- Misconfiguration: Incorrect DKIM signing settings within Office 365 cause validation problems.
- Content Alteration: Email content modifications in transit by middle servers invalidate DKIM signatures.
Key considerations
- Verify DNS: Ensure DKIM records are fully propagated across all DNS servers.
- Check Settings: Double-check the DKIM signing policy and enable it for correct domains and users.
- Investigate Mail Flow: Investigate potential mail flow issues or third-party programs altering email content.
Technical article
Documentation from Microsoft Docs explains that intermittent DKIM failures can occur if there are inconsistencies or propagation delays in your DNS records. Ensure that your DKIM records have fully propagated across all DNS servers.
15 Jun 2025 - Microsoft Docs
Technical article
Documentation from Microsoft Docs shares that one common cause of intermittent failures is incorrect configuration of the DKIM signing settings within Office 365. Double-check the signing policy and ensure it is enabled for the correct domains and users.
29 Oct 2022 - Microsoft Docs
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 resolve Microsoft Outlook S3140 errors blocking my transactional emails?
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?
How do I resolve a blocked sending IP with Office365 and what steps should I take to ensure transparency?
