What is a SMS "message unit?" Are Azure Communication SMS rate limits per number or per call to the API?

Question

The service limits page says that the rate limit for SMS is 200 requests or 200 message units per minute. Is a "message unit" every number that a SMS is sent to or is it only the requests that are sent, since up to 100 phone numbers can be included for one message? For example, if the same message is sent to 1500 phone numbers, and that is split up into 15 calls to the Azure Communications API of 100 numbers each, would that be rate limited since it is more than 200 numbers per minute, or would it not be rate limited since it is only 15 calls to the Azure API at the time?

Answer 1

Hello @jcr7c0 ,

According to the Azure Communication Services documentation, the rate limit for sending SMS messages is defined as both the number of requests and the number of message units per minute

This means a “message unit” refers to each individual message sent to a phone number.

So in your example of sending a single message to 1500 phone numbers split over 15 API requests, this would count as 1500 message units against the 200 message units per minute limit.

Even though there are only 15 total API requests, each request contains 100 recipients. So in total that is 15 * 100 = 1500 message units across those requests.

Since 1500 is greater than the 200 message units per minute limit, this send would be rate limited if done in under a minute.

If you need to send high volume of messages that exceed these rate limits, you would need to contact the ACS team at phone@microsoft.com as stated in the docs.

Best,

Grace