Service limits for Azure Communication Services

This document explains the limitations of Azure Communication Services APIs and possible resolutions.

Throttling patterns and architecture

When you hit service limitations, you will receive an HTTP status code 429 (Too many requests). In general, the following are best practices for handling throttling:

  • Reduce the number of operations per request.
  • Reduce the frequency of calls.
  • Avoid immediate retries because all requests accrue against your usage limits.

You can find more general guidance on how to set up your service architecture to handle throttling and limitations in the Azure Architecture documentation for throttling patterns. Throttling limits can be increased through a request to Azure Support.

  1. Go to Azure portal
  2. Select Help+Support
  3. Click on Create new support request
  4. In the Problem description, please choose Issue type as Technical and add in the details.

You can follow the documentation for creating request to Azure Support.

Acquiring phone numbers

Before acquiring a phone number, make sure your subscription meets the geographic and subscription requirements. Otherwise, you can't purchase a phone number. The below limitations apply to purchasing numbers through the Phone Numbers SDK and the Azure portal.

Operation Scope Timeframe Limit (number of requests)
Purchase phone number Azure tenant - 1
Search for phone numbers Azure tenant one week 5

Action to take

For more information, see the phone number types concept page and the telephony concept overview page.

If you want to purchase more phone numbers or place a special order, follow the instructions here. If you would like to port toll-free phone numbers from external accounts to their Azure Communication Services account, follow the instructions here.


Operation Timeframes (seconds) Limit (number of requests)
Create identity 30 1000
Delete identity 30 500
Issue access token 30 1000
Revoke access token 30 500
createUserAndToken 30 1000
exchangeTokens 30 500

Action to take

We recommend acquiring identities and tokens before creating chat threads or starting calls. For example, when the webpage loads or the application starts.

For more information, see the identity concept overview page.


When sending or receiving a high volume of messages, you might receive a 429 error. This error indicates you're hitting the service limitations, and your messages will be queued to be sent once the number of requests is below the threshold.

Rate Limits for SMS:

Operation Scope Timeframe (seconds) Limit (number of requests) Message units per minute
Send Message Per Number 60 200 200

Action to take

If you require to send a volume of messages that exceed the rate limits, email us at

For more information on the SMS SDK and service, see the SMS SDK overview page or the SMS FAQ page.


Sending a high volume of messages has a set of limitations on the number of email messages you can send. If you hit these limits, your messages won't be queued to be sent. You can submit these requests again, once the Retry-After time expires.

Rate Limits

Operation Scope Timeframe (minutes) Limit (number of emails)
Send Email Per Subscription 1 30
Send Email Per Subscription 60 100
Get Email Status Per Subscription 1 60
Get Email Status Per Subscription 60 200

Size Limits

Name Limit
Number of recipients in Email 50
Total email request size (including attachments) 10 MB

Action to take

This sandbox setup is designed to help developers begin building the application. Once the application is ready for production, you can gradually request to increase the sending volume. If you need to send more messages than the rate limits allow, submit a support request to raise your desired email sending limit. The reviewing team will consider your overall sender reputation, which includes factors such as your email delivery failure rates, your domain reputation, and reports of spam and abuse, when determining approval status.


Size Limits

Name Limit
Number of participants in thread 250
Batch of participants - CreateThread 200
Batch of participants - AddParticipant 200
Page size - ListMessages 200

Operation Limits

Operation Bucketed by Limit per 10 seconds Limit per minute
Create chat thread User 10 -
Delete chat thread User 10 -
Update chat thread Chat thread 5 -
Add participants / remove participants Chat thread 10 30
Get chat thread / List chat threads User 50 -
Get chat message User and chat thread 50 -
Get chat message Chat thread 250 -
List chat messages User and chat thread 50 200
List chat messages Chat thread 250 400
Get read receipts User and chat thread 5 -
Get read receipts Chat thread 250 -
List chat thread participants User and chat thread 10 -
List chat thread participants Chat thread 250 -
Send message / update message / delete message Chat thread 10 30
Send read receipt User and chat thread 10 30
Send typing indicator User and chat thread 5 15
Send typing indicator Chat thread 10 30

Chat storage

Azure Communication Services stores chat messages indefinitely till they are deleted by the customer.

Beginning in CY24 Q1, customers must choose between indefinite message retention or automatic deletion after 90 days. Existing messages remain unaffected, but customers can opt for a 90-day retention period if desired.


Accidentally deleted messages are not recoverable by the system.

Voice and video calling

PSTN Call limitations

Name Limit
Number of outbound concurrent calls 2

Call maximum limitations

Name Limit
Number of participants 350

Calling SDK streaming support

The Communication Services Calling SDK supports the following streaming configurations:

Limit Web Windows/Android/iOS
Maximum # of outgoing local streams that you can send simultaneously one video or one screen sharing one video + one screen sharing
Maximum # of incoming remote streams that you can render simultaneously 9 videos + one screen sharing 9 videos + one screen sharing

While the Calling SDK will not enforce these limits, your users may experience performance degradation if they're exceeded.

Calling SDK timeouts

The following timeouts apply to the Communication Services Calling SDKs:

Action Timeout in seconds
Reconnect/removal participant 120
Add or remove new modality from a call (Start/stop video or screen sharing) 40
Call Transfer operation timeout 60
1:1 call establishment timeout 85
Group call establishment timeout 85
PSTN call establishment timeout 115
Promote 1:1 call to a group call timeout 115

Action to take

For more information about the voice and video calling SDK and service, see the calling SDK overview page or known issues.

Teams Interoperability and Microsoft Graph

Using a Teams interoperability scenario, you'll likely use some Microsoft Graph APIs to create meetings.

Each service offered through Microsoft Graph has different limitations; service-specific limits are described here in more detail.

Action to take

When you implement error handling, use the HTTP error code 429 to detect throttling. The failed response includes the Retry-After response header. Backing off requests using the Retry-After delay is the fastest way to recover from throttling because Microsoft Graph continues to log resource usage while a client is being throttled.

You can find more information on Microsoft Graph throttling limits in the Microsoft Graph documentation.

Network Traversal

Operation Timeframes (seconds) Limit (number of requests)
Issue TURN Credentials 5 30000
Issue Relay Configuration 5 30000

Action to take

We recommend acquiring tokens before starting other transactions, like creating a relay connection.

For more information, see the network traversal concept overview page.

Next steps

See the help and support options.