DKIM Canonicalization Best Practices (relaxed vs simple)

Overview: Understand relaxed vs simple canonicalization to avoid false negatives and preserve integrity.

Prerequisites: Access to DKIM signer configuration.

Steps

1. Prefer relaxed/relaxed in most cases to handle benign whitespace changes.
2. Use simple only when you control all transformations end-to-end.
3. Test across MTAs and gateways that may rewrap headers.

Verification

• Signature validation: DKIM Checker
• Header diffs: Header Analyzer

Troubleshooting

• Failing signatures: switch body canonicalization to relaxed.
• MIME changes: ensure signer normalizes content consistently.

FAQ

Q: Does canonicalization affect DMARC? A: Indirectly; DKIM success is part of DMARC alignment.

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