Azure Communication Service Email Send Rate limit

Hi @87592231 Greetings! Thank you for posting this question here.

I apologize for the issue you are facing with Azure Communication Services.

why is rate limit not recovered after waiting more than one hour?

There are couple of things we can look into to understand why we see throttling limits even after waiting for a cooling period of 1 hour.

1. The throttling limits are set per subscription. If there are any other Email Communication Services resources created on the subscription, the throttling limits would factor in the Emails send by these services and apply the rate limit. Check your subscription and look up Email Communication Services to see if there are any other email services.
2. The rate limit differs between Custom Domains vs Azure Managed Domains. If your function app is designed to send emails to both domains , it could be possible that will get throttled sooner as Azure Managed domains have lower rates compared to Custom Domains. Please refer the below image for rate limits on Azure Managed Domains

Sometime ACS throwing 429 for an email and delivered the same email.

By default, the SDK is configured to retry the request upon receiving 429 throttling response, after waiting a certain period of time. You can a policy to your function app to prevent retrying and throw an error when throttling has reached. Refer the article Throw an exception when email sending tier limit is reached for the steps on implementing this.

You can further implement a logic to make ensure the delivery of the email by Subscribing to the Email events using Web Hook

If you identify your services need a higher throttling limit, you can put in a support request by following the steps provided in Quota increase for email domains

Hope this helps! If you need any additional assistance and help troubleshooting this further, please let us know and we would be happy to help you.

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