How do I request an increase to Azure Communication Services Email sending limits for a verified custom domain?

Mihir Srivastava 20 Reputation points Microsoft Employee
2026-08-14T08:29:33.31+00:00

We are using Azure Communication Services Email to send transactional email from a

verified custom domain, and we are hitting the default sending rate limits.

Current behaviour:

During a single controlled test run, the service accepted a batch of messages with

HTTP 202 and then began returning HTTP 429 (throttled) within the same hour. The

throttling started at approximately the documented default of 100 messages per hour.

Domain setup:

The sending domain is a customer-managed custom domain. Domain ownership, SPF, DKIM

and DKIM2 all show a Verified status in the portal.

What we are trying to achieve:

We are migrating existing, established outbound email volume from another provider

onto Azure Communication Services. Our steady-state requirement is several thousand

messages per hour, with a higher short-term per-minute peak because sends are

released on a schedule in batches rather than spread evenly across the day. The

default limits of 30 per minute and 100 per hour are well below what we already send

today.

Mail is transactional and recipient-scoped rather than bulk marketing, every message

includes a List-Unsubscribe header, and rollout is a staged ramp beginning with

low-volume batches in a non-production environment so bounce and complaint rates can

be monitored at each step.

Questions:

  1. What is the correct process to request an increase to the per-minute, per-hour and per-day email sending limits?
  2. Are these limits enforced per subscription, per domain, or per sender address? We want to confirm whether provisioning additional sender addresses would increase throughput, or whether a quota increase is the only available option.
  3. Is there a minimum sending-history or reputation period required before an increase will be considered, and if so, how is that period measured?
  4. Are there any domain configuration prerequisites beyond SPF and DKIM that should be in place before submitting the request?
Azure Communication Services
Answer accepted by question author
Praneeth Maddali 12,670 Reputation points Microsoft External Staff Moderator
2026-08-16T17:19:06.7566667+00:00

Hi @Mihir Srivastava

Thanks for the detailed information — that helps a lot.

You’re hitting the expected default rate limits for a verified custom domain in Azure Communication Services Email (30 messages per minute / 100 per hour). These limits are intentionally low for new senders so you can build reputation safely. Higher limits are available, but they require a manual quota increase request.

Answers to your questions

1. How to request the increase Follow the official process here: https://learn.microsoft.com/en-us/azure/communication-services/concepts/email/email-quota-increase

In short:

  • Prepare the questionnaire from that page (company details, subscription ID, ACS resource name, domain, email type, and the exact per-minute / per-hour / per-day volumes you need).
  • Create a support request in the Azure portal > Service and subscription limits (quotas) > Quota type: Azure Communication Services Email: Sending Limits. or

. Before you make the request, assess how many emails you plan to send. Consider key factors like:

  • Maximum messages per minute
  • Maximum messages per hour
  • Maximum messages per day

Please follow the below steps to create support request in Azure Portal.

Sign in to the Help + support - Microsoft Azure or go to https://portal.azure.com/#create/Microsoft.Support

Click on Create support request.

Enter quota in the box and click on 'Go'.

Search for Quota type: Select Service and Subscription Limits(Quotas) 

  1. Then click on Create a support request. Screenshot 2025-12-10 234101
  2. Select Quota type as Azure Communication Services Email: Sending Limits Screenshot 2025-12-10 225920

3.Click on "Next" Screenshot 2025-12-10 231151

4.Then provide the details as the requirement. Screenshot 2025-12-10 231411

  1. Next click on Save and Continue.
  2. You will see fields related to email sending quotas like region etc. Screenshot 2025-12-10 231913

Fill the details and Click on Review+Create.

  • Attach the completed questionnaire as a .txt file and submit.

Requests are reviewed manually (not auto-approved) and can take up to 72 hours.

2. Scope of the limits The limits are enforced per subscription, not per domain or per MailFrom address. Adding extra sender addresses will not increase throughput — a quota increase is the only way.

You can confirm the current defaults and scope in the service limits article: https://learn.microsoft.com/en-us/azure/communication-services/concepts/service-limits#email

3. Sending history / reputation requirements There’s no fixed “X days of history” requirement, but Microsoft does expect you to demonstrate good sender behaviour before approving higher limits. In practice this means:

  • Failure rate kept under 2% (ideally under 1% for larger increases)
  • Clean unsubscribe and bounce handling
  • Gradual volume ramp rather than a sudden jump

Your planned staged rollout with monitoring is exactly the right approach.

4. Additional domain prerequisites SPF + DKIM (and DKIM2) being verified is the main requirement, which you already have. Microsoft also strongly recommends configuring an MX record for the domain, even though ACS Email is outbound-only — domains without an MX record are more likely to be treated as spam by receiving providers.

Suggested next steps

  1. Fill out the questionnaire from the quota-increase article.
  2. Open the support request using the path above and attach the file.
  3. Continue your low-volume non-production testing while the request is reviewed so you keep building positive reputation.

Once the increase is approved, the new limits will apply to the subscription for that custom domain.

Let me know if you run into any issues creating the support request or if you need help with the wording of the questionnaire — happy to take a look.

Hope this helps!

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  1. AI answer

    2026-08-14T08:29:57.7533333+00:00
    1. The documented process is to submit a quota increase request through Azure Support. Steps:
      1. In the Azure portal, open Help + Support.
      2. Select Create new support request.
      3. In Describe your issue, enter Technical, then select Go.
      4. For Select a service, choose Service and Subscription Limits (Quotas).
      5. Select the relevant Issue type, Subscription, and Quota type.
      6. Add the requested details for the email quota increase and submit the request.
      The quota increase guidance also states that the request should be submitted as an incident report requesting a higher email sending limit.
    2. The default email sending rate limits are enforced per subscription, not per sender address. For verified custom domains, the documented default limits are:
      • Send Email: 30 per minute per subscription
      • Send Email: 100 per 60 minutes per subscription
      Provisioning additional sender addresses does not change those sending rate limits. Higher throughput requires a quota increase. The context also states that higher quotas are available only for verified custom domains, not Azure-managed domains.
    3. There is no fixed minimum sending-history period stated as a hard prerequisite, but the documented guidance is to gradually increase email volume over two to four weeks while monitoring delivery status. This is recommended so third-party email providers can adapt to the IP change and so sender reputation can be protected. For higher quota consideration, sender reputation is explicitly reviewed. The documented factors include:
      • delivery failure rates
      • domain reputation
      • spam and abuse reports
      One document states the failure rate must be less than 1% to enable a high email quota. Another quota increase document states requests are reviewed with failure rates expected to be below 2%. Both documents consistently indicate that low failure rates and good sender reputation are required for approval.
    4. Beyond SPF and DKIM, the documented prerequisite and recommendations are:
      • Use a verified custom domain rather than an Azure-managed domain.
      • Configure an MX record for the custom domain. Although Azure Communication Services Email supports outbound email only, an MX record is recommended because a custom domain without one might be labeled as spam and could damage sender reputation.
      • Build sender reputation before requesting the increase by sending legitimate production workload email and minimizing failures and spam rate.

    Additional points relevant to the scenario:

    • If requests exceed the current limit, Azure Communication Services returns HTTP 429 and requests can be retried after the Retry-After time passes.
    • The service is designed for high throughput and can support 1–2 million messages per hour when high throughput is enabled based on factors such as peak traffic, business need, failure-rate management, and domain reputation.

    References:

    AI-generated content may be incorrect. Read our transparency notes for more information.

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