ACS size limit

You cannot configure the 30 MB Azure Communication Services Email limit yourself; for a verified custom domain, submit an Azure Support request for approval. ^1^

Submit the request

1. In the Azure portal, open Help + Support.
2. Select Create a support request.
3. In Describe your issue, enter Technical, then select Go.
4. For Service, select Service and Subscription Limits (Quotas).
5. Select the subscription containing your ACS Email resource.
6. Choose the applicable Azure Communication Services email quota category. If the portal offers Other Requests, use it and state:
   • The ACS Email resource and verified custom domain.
   • Current limit: 10 MB.
   • Requested limit: 30 MB.
   • Business justification and expected attachment sizes.
7. Complete Additional details, review the request, and select Create. ^2^

A suitable description is:

Please increase the Azure Communication Services Email message/attachment size limit from 10 MB to 30 MB for the verified custom domain associated with this resource.

Requests are evaluated and are not automatically approved; evaluation can take up to 72 hours. Higher quotas are available only for verified custom domains, so your non-Azure-managed custom domain meets the domain-type prerequisite. ^1^

Account for Base64 encoding

The limit applies to the total email request, including attachments. Binary attachments are Base64 encoded, which increases their size by approximately 33%. Consequently, a 30 MB limit provides roughly 22–22.5 MB of usable binary attachment capacity, with slightly less available after accounting for the message body and other request content. ^1^

For files that cannot fit within the approved limit, store the file in Azure Blob Storage and email a time-limited shared access signature (SAS) link instead.

References

1. Service limits for Azure Communication Services
2. Help and support options for Azure Communication Services