feat(changelog): add new entry

Author: Changelog bot

changelog/january2025/2025-01-29-transactional-email-security-dkim-enhancement-stronger-.mdx

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+---
+title: DKIM Enhancement: Stronger Signature
+status: security
+author:
+    fullname: 'Join the #transactional-email channel on Slack.'
+    url: 'https://slack.scaleway.com'
+date: 2025-01-29
+category: managed-services
+product: transactional-email
+---
+
+We've improved email security by adding new headers to the DKIM signature. This strengthens authentication and enhances deliverability.
+- List-ID
+- List-Help
+- List-Owner
+- List-Post
+- List-Subscribe
+- List-Unsubscribe
+- List-Unsubscribe-Post
+- Message-ID
+