What causes invalid RSA public key errors in DKIM records and how can I fix it?

Key findings

• Malformed keys: A 'bad base64 decode' error strongly suggests that the DKIM public key is malformed in some way, preventing proper interpretation.
• Incorrect length: Base64 encoded data, including DKIM keys, should always have an even number of characters; an odd length indicates truncation or corruption.
• Copy-paste errors: The most common cause of malformed keys is truncation or corruption introduced during the process of copying and pasting the key into a DNS management interface.
• Hidden characters: Line-wrap in text editors or auto-cutting by DNS providers can introduce hidden characters or spaces that break the DKIM record.
• DNS migration impact: Switching DNS providers can be a common scenario where such errors occur if the key is not transferred precisely.

Key considerations

• Key verification: Always compare the published DKIM key against the original generated key to identify any missing or extra characters. This is a crucial step in troubleshooting DKIM failures.
• DNS record handling: Be cautious when copying DKIM keys, especially long ones, from sources that might introduce line breaks or truncate the string. Consider the advice on DKIM key issues with TXT record length limits.
• DNS propagation: After updating DKIM records, allow sufficient time for DNS propagation to complete before re-checking, as changes may not be immediately visible globally.
• Tool clarity: While DKIM validation tools are essential, their error messages may sometimes be technical, requiring an understanding of underlying issues like base64 decoding.

Key opinions

• Technical error complexity: Marketers frequently find technical error messages, like 'bad base64 decode', challenging to interpret without deeper technical guidance.
• Manual input sensitivity: There's a consensus that manually copying and pasting DKIM keys is a common point of failure, leading to truncation or corruption.
• Character integrity: Even missing a single character in the long DKIM string can cause the entire public key to be invalid, leading to authentication failures.
• DNS provider variations: Marketers report encountering issues with DNS providers that auto-cut DKIM records or introduce hidden characters during the publishing process.
• Domain and sender mismatch: A common 'DKIM signature not valid' error occurs when the DKIM signature domain does not match the sender domain, raising authenticity flags.
• Propagation delays: DNS propagation delays are acknowledged as a factor that can make immediate troubleshooting of DKIM record changes difficult.

Key considerations

• Thorough comparison: Always meticulously compare the published DKIM key in DNS with the originally generated key to catch subtle discrepancies. For example, understanding how to generate a a=rsa-sha256 key for DKIM is a starting point.
• Source integrity: Be mindful of the source from which DKIM keys are copied, ensuring no unintended line breaks or characters are introduced from text editors or other DNS records.
• DNS change management: When migrating DNS providers, pay extra attention to DKIM record accuracy, as this is a common time for new errors to surface.
• Diagnostic tools: Utilize reliable DKIM checkers to quickly validate your records and pinpoint specific issues, understanding that some tool errors might be vague. See also decoding DKIM temperror.

Key opinions

• Key malformation focus: Experts agree that 'bad base64 decode' errors fundamentally point to a malformed DKIM public key.
• Length validation: A key indication of corruption is an odd character count, as base64 encoded data should always have an even number of characters.
• Transcription errors: Truncation or corruption often occurs during the manual process of pasting the key into DNS management systems.
• Hidden character risk: Hidden control characters, line breaks (from text editors), or auto-splitting by DNS providers are frequent culprits in breaking DKIM records.
• DNS provider nuances: Different DNS providers may handle long TXT records in ways that inadvertently corrupt DKIM keys, requiring careful attention to their specific guidelines.

Key considerations

• Precise key matching: It is critical to ensure the DKIM public key published in DNS is an exact match to the private key used for signing, including every character. This relates to why DKIM might be failing.
• Avoiding manual errors: Whenever possible, use automated tools or direct integrations for publishing DKIM records to minimize human error during the copy-paste process. For instance, consider guidance on DKIM selector name examples.
• Understanding base64: A basic understanding of base64 encoding helps in identifying potential corruption in the key string, such as unexpected characters or incorrect length.
• Regular validation: Periodically validate DKIM records, especially after DNS changes or migrations, to catch issues early before they impact deliverability significantly.

Key findings

• Syntax validation: Documentation emphasizes that DKIM signatures are validated against the public key stored in the sender's DNS record, and any incorrect entry causes failure.
• Base64 encoding strictness: DKIM keys must be correctly base64 encoded; errors like 'bad base64 decode' indicate a fundamental formatting issue with the key string itself.
• Length management for TXT records: Long DKIM key values may exceed DNS TXT record length limits, requiring them to be split into multiple parts, each enclosed in double quotation marks and separated by a space.
• Authentication criteria: DKIM authentication fails if a signature cannot be found, if an existing one does not match, or if the published public key is invalid.
• Propagation delays: DNS propagation delays can temporarily cause 'signature not valid' errors until the updated record is globally recognized.

Key considerations

• Exact key replication: Ensure that the public key is copied and pasted exactly as generated, without any alterations, extra spaces, or hidden characters. This is paramount for DMARC, SPF, and DKIM setup.
• DNS TXT record formatting: If a DKIM key is too long for a single TXT record, it must be properly split and concatenated according to DNS standards to avoid 'CharacterStringTooLong' errors. Similar issues are covered when discussing fixing DKIM record published errors.
• DNS propagation awareness: Always account for DNS propagation delays, which can range from minutes to hours, before concluding that a DKIM record change has failed.
• Key rotation practices: When rotating DKIM keys, ensure both the old and new public keys are valid during the transition period to prevent disruption.