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Is DKIM signature case-sensitive and what causes DKIM tester errors?

6 Marketer opinions5 Expert opinions5 Technical articles3 Resources

Summary

DKIM (DomainKeys Identified Mail) aims to verify the sender's domain and ensure message integrity, preventing email spoofing and phishing. DKIM field names are case-insensitive, but field values, particularly the DKIM selector, *can* be case-sensitive. DKIM tester errors, however, are frequently due to the tester itself. Testers might be overly sensitive to case, or contain specific bugs around how they check DKIM records. When troubleshooting DKIM, always check DNS records, configurations and authentication headers directly. Common problems include incorrect DNS settings, typos in DKIM records, signing process failures, and DNS propagation delays. Not all email providers support DKIM signing, and DKIM can fail if email content is modified post-signing or if DNSSEC interferes. Best practice is to debug by inspecting Authentication-Results headers, using online validation tools, and testing across multiple providers like Gmail and Yahoo.

Key findings

  • DKIM Purpose: DKIM verifies sender domain and message integrity to prevent spoofing and phishing.
  • Case Sensitivity (Field Names): DKIM field names are case-insensitive, but field values, such as the selector, may be case-sensitive.
  • Tester Issues: DKIM failures reported *only* in testers are often due to bugs or overly-sensitive checks in the testers themselves.
  • Common Configuration Errors: Frequent causes include incorrect DNS settings, typos in DKIM records, and signing process problems.
  • External Factors: DNS propagation delays, lack of provider support for DKIM, content modification post-signing, and DNSSEC interference can also cause failures.

Key considerations

  • Prioritize Real-World Tests: If a tester reports a DKIM error, confirm the error with real email delivery to different providers before spending significant time troubleshooting.
  • Check the Authentication-Results Header: This provides detailed information about the DKIM verification process.
  • Use Online Validation Tools: Validate DKIM records and signatures using reputable online tools.
  • Verify Configuration and Signing: Ensure the email server is properly configured and signing messages with DKIM.
  • Consider DNSSEC: If using DNSSEC, confirm it is correctly configured and not interfering with DKIM.

What email marketers say
6Marketer opinions

DKIM signature validation can fail due to various reasons, including case-sensitivity of the DKIM selector, errors in the DKIM record (incorrect syntax, key length, or value), DNS propagation delays, and issues with the email server's configuration or signing process. Not all email providers support DKIM signing, and DKIM can fail if the email content is modified after signing. Using DKIM validators and testing across different email providers are crucial for ensuring correct DKIM setup.

Key opinions

  • Case Sensitivity: The DKIM selector is case-sensitive; ensure it matches the DNS record.
  • Record Errors: Common errors include incorrect key length, key value, and syntax in the DKIM record.
  • DNS Propagation: DNS propagation delays can lead to temporary DKIM failures.
  • Server Configuration: Ensure the sending server is properly configured to sign outgoing messages.
  • Content Modification: DKIM can fail if the email content is modified after signing.
  • Provider Support: Not all email providers support DKIM signing.

Key considerations

  • Validation Tools: Use DKIM validators to identify errors in your DKIM setup.
  • Testing: Test DKIM across different email providers (Gmail, Yahoo, etc.) to ensure it works correctly.
  • Record Accuracy: Double-check the syntax and values in your DKIM DNS record.
  • Server Configuration: Verify that your email server is correctly signing outgoing messages with DKIM.
Marketer view

Email marketer from MXToolbox shares that DNS record syntax errors, incorrect key values, and issues with the signing process are common. They recommend using their online tools to check DKIM records and diagnose problems.

April 2022 - MXToolbox
Marketer view

Email marketer from DKIMValidator.com says that not all email providers support DKIM signing, and ensuring your sending server is properly configured to sign outgoing messages is essential. Using a DKIM validator can help identify errors.

December 2021 - DKIMValidator.com
Marketer view

Email marketer from Reddit suggests using online DKIM validators and sending test emails to different email providers (Gmail, Yahoo, etc.) to ensure DKIM is working correctly across various platforms.

August 2021 - Reddit
Marketer view

Email marketer from EmailDrips explains that DKIM can fail if the email content is modified after signing, if the DNS record is incorrect or inaccessible, or if there are issues with the email server's configuration.

May 2021 - EmailDrips
Marketer view

Email marketer from SuperUser explains that common errors include incorrect key length, incorrect key value, and missing semicolons. DNS propagation delays can also lead to temporary failures.

June 2023 - SuperUser
Marketer view

Email marketer from StackOverflow states that the DKIM selector is case-sensitive, and if the selector in your email doesn't match the one in your DNS record, DKIM will fail.

June 2023 - StackOverflow

What the experts say
5Expert opinions

DKIM tester errors can arise from various sources. The SFMC DKIM key may appear correct, but testers might be overly sensitive to case variations in the 'from' address, unlike typical ISPs. If DKIM failures are isolated to the tester, it likely indicates a bug in the testing tool itself. One identified bug is a failure when the domain in the 'd=' and 'i=' fields differ in case. Outside of tester issues, common causes include incorrect syntax (missing semicolons, spacing) in the DKIM record and DNS propagation delays.

Key opinions

  • SFMC DKIM Key: SFMC DKIM keys may appear valid.
  • Tester Sensitivity: Testers might be more sensitive to case variations than ISPs.
  • Tester Bugs: Failures only in testers likely indicate a bug in the tester application.
  • Case Mismatch Bug: A specific bug exists where testers fail if the domain in the 'd=' and 'i=' fields differ in case.
  • Syntax Errors: Incorrect syntax in the DKIM record is a common cause of errors.
  • DNS Propagation: DNS propagation delays can lead to temporary failures.

Key considerations

  • Check with Gmail: Verify DKIM validity by sending emails to Gmail to bypass potential tester sensitivities.
  • Isolate the Issue: Determine if the DKIM failure is isolated to specific testers or affects real-world deliverability.
  • Review DKIM Record: Carefully review the DKIM record for correct syntax, including semicolons and spacing.
  • Wait for Propagation: Allow sufficient time for DNS changes to propagate before troubleshooting.
Expert view

Expert from Email Geeks confirms it is a tester bug, specifically failing if the domain in the d= and in the i= differ in case, and indicates a fix is coming.

December 2022 - Email Geeks
Expert view

Expert from Spamresource.com explains that a common cause of DKIM tester errors is incorrect syntax in the DKIM record, such as missing semicolons or incorrect spacing. Also, DNS propagation delays can temporarily cause verification failures.

February 2024 - Spamresource.com
Expert view

Expert from Email Geeks says that if failures aren’t seen elsewhere, it can be written off as a bug in the tester.

February 2022 - Email Geeks
Expert view

Expert from Email Geeks suggests the tester might be sensitive to the upper/lowercase of the visible from address, unlike ISPs, and recommends checking with Gmail.

May 2021 - Email Geeks
Expert view

Expert from Email Geeks recognizes the SFMC DKIM key and says it looks OK.

August 2023 - Email Geeks

What the documentation says
5Technical articles

DKIM aims to verify the sender's domain and ensure message integrity, preventing spoofing and phishing. DKIM field names are case-insensitive, but field values might be case-sensitive. Common issues include incorrect DNS settings, typos in DKIM records, signing process problems, stricter receiver requirements, and DNSSEC interference. Debugging involves inspecting the Authentication-Results header, using online validation tools, and correctly configuring DNS records.

Key findings

  • DKIM Purpose: DKIM verifies the sender's domain and ensures message integrity.
  • Case Sensitivity: DKIM field names are case-insensitive, but field values may be case-sensitive.
  • Common Issues: Incorrect DNS settings, typos in DKIM records, and signing process problems are common.
  • Receiver Requirements: Some receiving mail servers have stricter DKIM requirements.
  • DNSSEC Interference: DNSSEC can interfere with DKIM record verification.

Key considerations

  • DNS Configuration: Ensure DNS settings and DKIM records are correctly configured.
  • Authentication-Results Header: Check the Authentication-Results header for debugging.
  • Online Validation: Use online tools to verify the DKIM signature.
  • Signing Process: Address any problems with the email signing process.
  • Stricter Requirements: Be aware of stricter DKIM requirements from some receivers.
Technical article

Documentation from Port25 says that debugging DKIM involves checking the Authentication-Results header, verifying the DKIM signature with online tools, and ensuring the DNS records are correctly configured.

February 2023 - Port25
Technical article

Documentation from Wikipedia explains that DKIM is designed to verify the domain name associated with a message and confirm that the message content has not been altered during transit, which helps prevent email spoofing and phishing.

May 2021 - Wikipedia
Technical article

Documentation from AuthSMTP explains that incorrect DNS settings, typos in the DKIM record, and problems with the signing process on the sending server are common DKIM issues. Also, some receiving mail servers may have stricter requirements than others.

August 2021 - AuthSMTP
Technical article

Documentation from RFC Editor explains that DKIM field names are case-insensitive, but field values might be case-sensitive depending on the specific field.

July 2024 - RFC Editor
Technical article

Documentation from Cloudflare indicates that issues with DKIM DNS records being set up incorrectly, or DNSSEC interfering with record verification can cause testers to incorrectly report errors.

November 2023 - Cloudflare

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3Resources

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