Summary
Interpreting SpamAssassin DKIM test results and troubleshooting signature issues requires a multifaceted approach, encompassing DNS configuration checks, signature validation using tools, domain alignment verification, and awareness of potential issues like DNS propagation delays, TXT record length limits, and canonicalization algorithm errors. Additionally, factors external to DKIM, such as sender reputation and email forwarding, can significantly impact deliverability. Using manual testing and preview tools aids in identifying root causes.
Key findings
- SpamAssassin Tests: The `DKIM_SIGNED` test indicates a DKIM signature is present, while `DKIM_INVALID_DKIM` signifies an invalid signature.
- DNS Configuration: Incorrect DNS settings (typos, selector issues) are a common cause. Verify DKIM TXT records against signing keys.
- Domain Alignment: DKIM requires the signing domain to align with the 'From' header domain.
- Transit Issues: Modifications to email content during transit invalidate DKIM signatures.
- DNS Propagation: Ensure full DNS propagation; outdated information can cause failures.
- Record Limits: DNS TXT record length limitations can truncate DKIM records, causing failures.
- Key Size: Inadequate DKIM key sizes (less than 2048 bits recommended) can lead to failures.
- DMARC Compliance: DKIM is crucial for DMARC alignment and achieving 'Pass' results.
- Sender Reputation: Poor sender reputation can negatively impact deliverability, independent of DKIM.
- Canonicalization: Incorrect canonicalization algorithms can invalidate the DKIM signature.
- DNS resolution failures: Temporary DNS resolution issues may cause verification failures.
Key considerations
- Use Analysis Tools: Employ tools like aboutmy.email and MXToolbox to identify and validate DKIM signatures and DNS records.
- Inspect Headers: Utilize preview tools to inspect email headers and diagnose DKIM issues.
- Manual Testing: Use OpenDKIM tools for manual signing and verification to isolate problems.
- Monitor DNS: Regularly check DNS server status and network connectivity.
- Review Algorithms: Ensure correct header and body canonicalization methods are employed.
- Maintain Reputation: Adhere to email best practices to maintain a positive sender reputation.
- DKIM record syntax: Ensure the DKIM record itself has correct syntax and proper selectors.
What email marketers say
8 marketer opinions
Interpreting SpamAssassin DKIM test results and troubleshooting DKIM signature issues involves verifying DNS configuration, ensuring proper domain alignment, checking for DNS propagation issues, using DKIM record lookup tools, and addressing limitations related to TXT record length and key size. Email forwarding and modifications during transit can also invalidate DKIM signatures. Analyzing email headers and using preview tools can aid in diagnosing the root cause.
Key opinions
- DNS Configuration: Incorrect DNS settings (typos, selector issues) are a common cause of DKIM failures. Verify the DKIM TXT record against the signing key.
- Forwarding Invalidation: Email forwarding can alter headers, invalidating the DKIM signature.
- DNS Propagation: Ensure the DKIM record is fully propagated across all DNS servers.
- Domain Alignment: DKIM requires the signing domain to align with the domain in the 'From' header.
- Record Limitations: DNS providers may impose limitations on TXT record length, potentially truncating DKIM records. Consider splitting the record if possible.
- Key Size: Insufficient DKIM key sizes (less than 1024 bits) can lead to failures. Use a key size of at least 2048 bits.
Key considerations
- Use Lookup Tools: Employ tools like MXToolbox to identify errors in the DKIM record's syntax.
- Analyze Headers: Use preview tools to inspect email headers and troubleshoot DKIM issues.
- Transit Modification: Be aware that modifications to email content during transit can invalidate DKIM signatures.
Marketer view
Email marketer from EmailOnAcid describes that some DNS providers have limitations on the length of TXT records, potentially truncating the DKIM record and causing verification failures. Splitting the DKIM record into multiple TXT records (if supported by the DNS provider) can resolve this issue.
30 Aug 2022 - EmailOnAcid
Marketer view
Email marketer from GlockApps explains that using an insufficient DKIM key size (e.g., less than 1024 bits) can lead to DKIM failures. Using a key size of at least 2048 bits is recommended for better security and compliance with modern email standards.
9 Apr 2022 - GlockApps
What the experts say
4 expert opinions
Interpreting SpamAssassin DKIM results and troubleshooting involves understanding the specific tests (DKIM_SIGNED vs DKIM_INVALID_DKIM), using tools to analyze signatures (like aboutmy.email), ensuring proper domain alignment between signing domain and From header, and recognizing that DKIM is crucial for DMARC compliance and overall deliverability. Failures can stem from record syntax errors or modifications during transit.
Key opinions
- SpamAssassin Tests: `DKIM_SIGNED` indicates a DKIM signature header is present. `DKIM_INVALID_DKIM` signifies the signature is invalid.
- Domain Alignment: DKIM signatures must align with the domain in the 'From' header for successful verification and DMARC compliance.
- Transit Issues: Modifications to the message content during transit after signing can cause DKIM failures.
- DMARC Dependence: DKIM plays a critical role in DMARC alignment, contributing to improved deliverability and authentication results.
Key considerations
- Use Analysis Tools: Utilize tools like aboutmy.email to gain detailed insights into DKIM signature issues.
- Check Record Syntax: Ensure the DKIM record itself has correct syntax and proper selectors.
Expert view
Expert from SpamResource explains that DKIM failures can occur if the signing domain does not match the domain in the From header, or if the message content is modified in transit after signing. It also notes that issues can arise from problems in the DKIM record itself, such as incorrect syntax or missing selectors.
25 Apr 2024 - SpamResource
Expert view
Expert from Word to the Wise highlights that DKIM is essential for DMARC alignment and achieving 'Pass' results. It emphasizes the importance of having a valid DKIM signature that aligns with the domain used in the 'From' header, in order to improve email deliverability and authentication.
5 Apr 2024 - Word to the Wise
What the documentation says
5 technical articles
Interpreting SpamAssassin DKIM test results involves understanding that DKIM_SIGNED indicates a signature's presence, while DKIM_INVALID signals a validity problem. DNS resolution failures can cause transient issues. Manual testing with OpenDKIM tools can help isolate problems, and correct implementation of canonicalization algorithms is vital. Poor sender reputation, although not DKIM-specific, can still impact deliverability.
Key findings
- SpamAssassin DKIM Tests: DKIM_SIGNED means a DKIM signature is present; DKIM_INVALID suggests it's not valid.
- DNS Resolution: Temporary DNS issues can lead to DKIM verification failures.
- Canonicalization: Incorrect canonicalization algorithms invalidate DKIM signatures.
- Sender Reputation: Poor sender reputation can contribute to spam classification, regardless of DKIM status.
Key considerations
- Manual Testing: Use OpenDKIM tools for manual signing and verification to isolate issues.
- Monitor DNS: Check DNS server status and network connectivity.
- Maintain Reputation: Employ good email practices to maintain a positive sender reputation.
Technical article
Documentation from RFC Editor shares that the wrong choice or implementation of DKIM canonicalization algorithms can invalidate the signature. The header and body canonicalization methods must be handled correctly during signing and verification.
3 Oct 2024 - RFC Editor
Technical article
Documentation from SpamAssassin Wiki explains that a DKIM_SIGNED test indicates the presence of a DKIM signature header. A DKIM_INVALID test (or similar) indicates a problem with the signature's validity. These tests alone do not guarantee spam classification but contribute to the overall score.
24 May 2023 - SpamAssassin Wiki
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