Summary
DKIM failures in Microsoft while passing in Gmail and Yahoo can be attributed to a multitude of factors. Microsoft's stricter DKIM validation, reputation filtering, and sensitivity to RFC specification deviations are key. Technical issues such as message alteration during transit, DNSSEC misconfiguration, incorrect DKIM record setup (including key length, whitespace, and long lines), DNS propagation delays, and DMARC alignment problems can also cause failures. Additionally, Microsoft's use of feedback loops and content analysis can result in penalties for spam complaints or suspicious email content, even with a valid DKIM signature. Thorough testing, reputation monitoring, and adherence to best practices are essential for troubleshooting.
Key findings
- Stricter Validation: Microsoft employs more stringent DKIM validation processes compared to other providers.
- Reputation Filtering: Email deliverability can be affected by Microsoft's reputation filtering, even with valid DKIM signatures.
- RFC Sensitivity: Microsoft's DKIM implementation is more sensitive to minor deviations from RFC specifications, especially canonicalization algorithms.
- Technical Issues: Failures can result from message alteration, DNSSEC misconfiguration, incorrect DKIM record setup, or DNS propagation delays.
- Feedback Loops: Microsoft uses feedback loops, and spam complaints can lead to penalties, even with a valid DKIM signature.
- Content Analysis: Microsoft analyzes email content; spam-like content or suspicious links can cause failures.
- DMARC Alignment: Lack of SPF and DKIM alignment can lead to DMARC failures, impacting deliverability.
Key considerations
- Test Thoroughly: Conduct thorough DKIM setup tests with various email clients, particularly Microsoft Outlook and Office 365.
- Monitor Reputation: Actively monitor IP and domain reputation, especially using Microsoft's SNDS program.
- Check DNSSEC: Verify proper DNSSEC configuration and troubleshoot any related issues.
- Optimize DKIM Record: Ensure the DKIM TXT record is correctly set up, with no long lines, whitespace errors, or typographical errors.
- Inspect Headers: Check for any modifications in message headers that could indicate message alteration.
- Align DMARC: Ensure proper SPF and DKIM alignment for DMARC compliance.
- Review Content: Analyze email content for spam-like characteristics and suspicious elements.
- Monitor FBLs: Monitor Microsoft's feedback loops and address any spam complaints promptly.
- Canonicalization Algorithms: Carefully review and ensure correct implementation of canonicalization algorithms ('h=' and 'b=' tags) in your DKIM signature.
What email marketers say
8 marketer opinions
DKIM failures in Microsoft, despite passing in Gmail and Yahoo, can stem from Microsoft's stricter validation standards, reputation filtering, DNSSEC issues, or problems with DKIM record format and DNS resolution. Testing DKIM setup, monitoring IP and domain reputation, and ensuring proper SPF/DKIM alignment are crucial for resolving these issues. Microsoft also analyzes email content and uses feedback loops, so content and reputation are important factors.
Key opinions
- Stricter Validation: Microsoft's DKIM validation is more stringent than other providers, leading to failures even with minor issues in the DKIM signature or DNS record.
- Reputation Filtering: Microsoft applies reputation filtering, potentially flagging emails with poor domain/IP reputation even if the DKIM signature is valid.
- DNSSEC Issues: Broken DNSSEC configurations can interfere with DKIM validation, causing failures specifically in Microsoft's email systems.
- DKIM Record Format: Long lines in the DKIM TXT record can cause resolution problems with Microsoft's servers.
- Content Analysis: Microsoft analyzes email content, and spam-like content can trigger flags despite a valid DKIM signature.
- SPF/DKIM Alignment: Lack of SPF and DKIM alignment can lead to DMARC failures, causing Microsoft to treat emails as suspicious.
Key considerations
- Thorough Testing: Test DKIM setup using various email clients, specifically Microsoft Outlook and Office 365, to identify discrepancies.
- Reputation Monitoring: Monitor both IP and domain reputation, especially with Microsoft's SNDS program, to identify and address reputation issues.
- DNSSEC Checks: Check for DNSSEC-related issues using tools like MXToolbox's DNSSEC tool.
- DKIM Record Optimization: Break up long lines in the DKIM TXT record to improve compatibility.
- Content Review: Analyze email content for spam-like characteristics using tools like mail-tester.com.
- DMARC Alignment: Ensure proper SPF and DKIM alignment for DMARC compliance to improve deliverability.
Marketer view
Email marketer from SendGrid explains the importance of SPF and DKIM alignment for passing DMARC checks. While DKIM might pass individually, failing DMARC due to alignment issues could lead Microsoft to treat the email as suspicious. They advise ensuring proper SPF and DKIM alignment to improve deliverability.
8 Jun 2023 - SendGrid
Marketer view
Email marketer from Email on Acid stresses the importance of testing your DKIM setup using various email clients, including Microsoft Outlook and Office 365. They advise using Email on Acid's platform to send test emails and analyze the results, helping to identify any discrepancies or configuration errors.
11 May 2022 - Email on Acid
What the experts say
3 expert opinions
DKIM failures in Microsoft, despite passing elsewhere, are attributed to several factors. One thread suggests exploring past discussions for explanations. Word to the Wise highlights Microsoft's stricter adherence to RFC specifications, particularly regarding canonicalization algorithms. Spam Resource emphasizes the role of Microsoft's feedback loops; spam complaints can lead to penalties even with a valid DKIM signature, potentially causing suppressed emails and perceived DKIM failures.
Key opinions
- Stricter RFC Adherence: Microsoft's DKIM implementation is more sensitive to deviations from RFC specifications, particularly concerning canonicalization algorithms.
- Feedback Loop Impact: Microsoft's feedback loops can penalize domains based on spam complaints, even if DKIM is technically valid, leading to suppressed emails.
Key considerations
- Review Canonicalization: Carefully review and ensure correct implementation of canonicalization algorithms ('h=' and 'b=' tags) in your DKIM signature.
- Monitor Feedback Loops: Monitor Microsoft's feedback loops and address spam complaints promptly to avoid penalties and email suppression.
Expert view
Expert from Word to the Wise responds that Microsoft's DKIM implementation is known to be more sensitive to minor deviations from the RFC specifications. Specifically, they recommend ensuring that the canonicalization algorithms specified in your DKIM signature ('h=' and 'b=' tags) are correctly implemented. Microsoft's servers may be less forgiving of relaxed canonicalization than other providers.
6 Jan 2023 - Word to the Wise
Expert view
Expert from Email Geeks shares a thread discussing why DKIM may fail at Microsoft while passing everywhere else. The URL for the thread is https://emailgeeks.slack.com/archives/C0Y3T12Q0/p1668786804486909.
14 Aug 2023 - Email Geeks
What the documentation says
4 technical articles
DKIM failures in Microsoft, while passing in Gmail and Yahoo, are attributed to several potential technical issues. Message alteration during transit, incorrect DKIM record setup, incorrect key lengths, whitespace errors, DNS propagation delays, DNS lookup failures, incorrect subdomain setup, typographical errors, and deviations from the DKIM standard (RFC 6376) can all cause verification to fail, especially when Microsoft's servers check the DKIM record.
Key findings
- Message Alteration: Messages altered in transit can invalidate the DKIM signature.
- DKIM Record Issues: Incorrect DNS record setup, key length, whitespace errors, and typographical errors in the DKIM record can cause failures.
- DNS Propagation: DNS propagation delays and DNS lookup failures can lead to intermittent DKIM failures.
- RFC Non-Compliance: Deviations from the RFC 6376 standard for DKIM signatures result in verification failures.
Key considerations
- Header Inspection: Check message headers for modifications indicating alteration during transit.
- DKIM Record Validation: Ensure correct DKIM record setup, including key length, and eliminate whitespace or typographical errors.
- DNS Verification: Verify proper DNS propagation and troubleshoot any DNS lookup failures.
- RFC Compliance: Adhere strictly to the RFC 6376 standard for DKIM signature format and syntax.
Technical article
Documentation from dkim.org lists potential issues such as incorrect key length, whitespace errors in the DKIM record, and DNS propagation delays. These factors can cause intermittent DKIM failures, particularly when Microsoft's servers check the DKIM record.
5 Feb 2022 - dkim.org
Technical article
Documentation from AuthSMTP lists potential issues such as incorrect DNS record setup, DNS propagation delays, and DNS lookup failures as reasons for DKIM failure. They also explain that a failure to have the correct subdomain set up with the correct key or any typographical errors in the DKIM record can cause failure.
13 Jun 2022 - AuthSMTP
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