Azure Communication Services Email SMTP custom domain — limit for MailFrom / From addresses

Faisal Riaz 175 Reputation points
2026-06-19T06:15:07.8166667+00:00

Hello Microsoft Support Team,

I am using Azure Communication Services Email with SMTP and a custom verified domain.

Example configuration:

  • Custom domain: gt.co.uk
  • Current MailFrom / From address: ******@gt.co.uk
  • Display name: UAT
  • Sending method: SMTP

I want to add and use multiple MailFrom / From addresses under the same custom domain, for example:

  • ******@gt.co.uk
  • ******@gt.co.uk
  • ******@gt.co.uk
  • ******@gt.co.uk

Can you please confirm the maximum number of MailFrom / SenderUsername / From addresses that can be added for a single custom domain in Azure Communication Services Email?

I found documentation that appears to mention a limit of 100 SenderUsername / MailFrom resources per domain, but I would like to confirm:

  1. Does this limit apply to SMTP sending as well?
  2. Is the limit 100 per custom domain or per Email Communication Service resource?
  3. Are there any additional prerequisites, such as increasing the default sending limit before multiple MailFrom addresses can be added?
  4. Can each configured MailFrom address be used as the From address when sending emails through SMTP?

Thank you.Hello Microsoft Support Team,

I am using Azure Communication Services Email with SMTP and a custom verified domain.

Example configuration:

  • Custom domain: gt.co.uk
  • Current MailFrom / From address: ******@gt.co.uk
  • Display name: Admin

I want to add and use multiple MailFrom / From addresses under the same custom domain, for example:

  • ******@gt.co.uk
  • ******@gt.co.uk
  • ******@gt.co.uk
  • ******@gt.co.uk

Can you please confirm the maximum number of MailFrom / SenderUsername / From addresses that can be added for a single custom domain in Azure Communication Services Email?

I found documentation that appears to mention a limit of 100 SenderUsername / MailFrom resources per domain, but I would like to confirm:

  1. Does this limit apply to SMTP sending as well?
  2. Is the limit 100 per custom domain or per Email Communication Service resource?
  3. Are there any additional prerequisites, such as increasing the default sending limit before multiple MailFrom addresses can be added?
  4. Can each configured MailFrom address be used as the From address when sending emails through SMTP?

Thank you.

Azure Communication Services

Answer accepted by question author

Praneeth Maddali 10,705 Reputation points Microsoft External Staff Moderator
2026-06-19T08:27:53.84+00:00

Hi @Faisal Riaz

Thank you for reaching out and for providing the clear details about your Azure Communication Services Email setup with the gt.co.uk custom domain.

Based on the current Microsoft documentation, here are the clarifications to your questions:

MailFrom / SenderUsername limit

Yes — you can configure multiple sender addresses under the same verified custom domain.

Azure Communication Services supports up to 100 MailFrom (SenderUsername) resources per custom domain. This means your domain (gt.co.uk) can have up to 100 unique sender addresses.

Does this limit apply to SMTP?

Yes — the limit applies at the domain resource level. The same configured MailFrom (SenderUsername) resources work for both SMTP and API/SDK sending methods.

Scope of the limit The limit is per custom domain, not per Email Communication Service resource.

Prerequisite to add multiple MailFrom addresses Before adding additional sender addresses, ensure that:

  • Your domain is verified
  • Your email sending quota has been increased (if you're still on the default tier)

In many cases, the “Add MailFrom” button is disabled until the quota is raised.

To request a quota increase: Go to the Azure Portal > Help + support > New support request > Service and subscription limits (quotas). Mention your need to enable multiple sender usernames on your custom domain.

Using MailFrom addresses with SMTP Each configured MailFrom (SenderUsername) represents a valid sender identity. You can use any of these configured addresses as the From address when sending via SMTP. Sending from unconfigured addresses is not supported.

Reference :

https://learn.microsoft.com/en-us/azure/communication-services/concepts/service-limits

https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/email/add-multiple-senders?pivots=platform-azp

https://learn.microsoft.com/en-us/azure/communication-services/concepts/email/email-quota-increase

https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/email/send-email-smtp/smtp-authentication?tabs=built-in-role

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