@Marc Rufer Thanks for reaching out. As you mentioned, system topics in Event Grid do not use SAS keys for authentication. System topics are created automatically by Azure services and are used for monitoring and alerting purposes. They are not intended to be used for custom event handling scenarios, and therefore do not require SAS keys.
If you are only using system topics in Event Grid, you can safely ignore the email about regenerating your SAS key. However, if you are using custom topics or subscriptions in Event Grid, you will need to regenerate your SAS key on or after August 15, 2024 to ensure continued access to Event Grid.
I hope this helps! Let me know if you have any further questions.