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Can I use the same verified custom domain on multiple Azure Communication Services Email resources in different subscriptions?

S H 60 Reputation points
2026-05-07T10:41:54.3566667+00:00

Hi Microsoft Team and Community,

I have a custom domain MyDomain.com that is already fully verified (SPF, DKIM, DKIM2) on one Email Communication Service in Subscription A. The sender ******@MyDomain.com is working fine and landing in Inbox.

Now I want to create a second Email Communication Service in Subscription B (same tenant) and use the same domain with a new sender ******@MyDomain.com.
My questions are:

  1. Do I need to re-verify the domain again (new TXT record) in the second Email Communication Service?
  2. Since the DNS records (SPF/DKIM) already exist, will the second ECS automatically use them?
  3. What is the recommended way to share one custom domain across multiple ECS resources in different subscriptions?
  4. Any known limitations or best practices for this scenario?

I would appreciate any official documentation or real experience on this.

Thanks in advance!

Azure Communication Services
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Answer accepted by question author

Praneeth Maddali 10,290 Reputation points Microsoft External Staff Moderator
2026-05-07T18:07:23.94+00:00

Hi @S H

Thank you for your detailed question and for providing all the context

No, You cannot directly share the same verified custom domain resource across different Email Communication Services (ECS) in separate subscriptions. You will need to provision and verify the domain again in Subscription B.

  1. Do I need to re-verify the domain again (new TXT record) in the second Email Communication Service?
    Yes. You must add the domain (MyDomain.com) to the new ECS in Subscription B and complete the ownership verification. Azure will provide a new unique TXT record for this instance. You can add this new TXT record alongside the existing one from Subscription A — they coexist without conflict.
  2. Since the DNS records (SPF/DKIM) already exist, will the second ECS automatically use them?
    Partially yes. Your existing SPF, DKIM, and DKIM2 records (at the DNS level) can be reused, as they authorize Azure’s sending infrastructure. However, you still need to go through the full provisioning and verification process in the second ECS so Azure can associate and validate them for that specific resource.
  3. What is the recommended way to share one custom domain across multiple ECS resources in different subscriptions?
    • Provision the custom domain independently in each ECS (repeat the add + verify steps).
    • Once verified in each ECS, connect the domain to your Azure Communication Services resource (you can filter by subscription when connecting). A single Communication Services resource supports linking up to 100 custom domains.
  4. Any known limitations or best practices? Limitations: Domain resources are scoped per Email Communication Service. There is no automatic cross-subscription sharing of the verified domain object. Best practices:
    • Use subdomains (e.g., prod.mydomain.com and marketing.mydomain.com) for different environments or subscriptions — this provides better isolation.
    • Where possible, consolidate into a single ECS and add multiple sender addresses (donotreply@ and donotreply2@) under the same domain.
    • Fully test deliverability after setup.
    • Align data locations/geographies between resources

reference:

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

https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/email/connect-email-communication-resource?pivots=azure-portal

https://learn.microsoft.com/en-us/azure/communication-services/concepts/email/email-domain-and-sender-authentication

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

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Answer accepted by question author

Golla Venkata Pavani 5,920 Reputation points Microsoft External Staff Moderator
2026-05-07T11:54:23.4566667+00:00

Hi @S H

Thank you for reaching us regarding the issue.

No, you cannot directly share the same verified custom domain resource across multiple Email Communication Service (ECS) resources without re-provisioning it. Domain resources are child resources scoped to a specific ECS.

  1. Do I need to re-verify the domain again (new TXT record) in the second Email Communication Service?
    Yes, You must provision the custom domain and complete ownership verification (new unique TXT record) separately in each Email Communication Service.
  2. Since the DNS records (SPF/DKIM) already exist, will the second ECS automatically use them?
    Partially yes. SPF and DKIM records (DNS-level) can be reused. However, ownership verification (TXT) and full provisioning must be done again in the second ECS.
  3. What is the recommended way to share one custom domain across multiple ECS resources in different subscriptions?
    Provision the same custom domain independently in each ECS (repeat verification), then connect the verified domain to your Communication Services resource (filter by subscription/ECS when connecting). Up to 100 custom domains can be linked to one Communication Services resource.
  4. Any known limitations or best practices for this scenario?
  • Limitation: Domains are scoped to a specific Email Communication Service; no automatic sharing.
  • Best practices: Prefer one ECS when possible. Use subdomains for isolation. Add multiple sender usernames under one domain. Ensure matching geography/data location.

Reference:
https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/email/add-custom-verified-domains?pivots=platform-azp
https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/email/connect-email-communication-resource?pivots=azure-portal

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  1. AI answer

    2026-05-07T10:42:15.29+00:00

    A single custom domain is provisioned and verified inside Azure Communication Services Email as a domain resource, and then linked to one Email Communication Service resource at a time. The domain object (with its verification and sender authentication state) is what is shared, not the DNS records alone.

    From the provided documentation:

    • A custom domain must be added and verified (ownership TXT + SPF/DKIM) in Email Communication Services before it can be used to send email.
    • Each Email Communication Service resource is then linked with one of the verified domains from Email Communication Services: “Application Integration linked with Azure Communication Service and each communication service can be linked with one of verified domains from Email Communication Services.”

    Given this model, the implications for the questions are:

    1. Re-verification for a second ECS resource
      The domain is verified at the Email Communication Services domain level, not per ECS resource. Once the domain is provisioned and verified as a custom domain, it is “ready to send emails using the custom domain.” A second ECS resource would not require a different TXT/SPF/DKIM set; it would reuse the same verified domain object. The verification step is only needed to get the domain into the Verified/Enabled state initially.
    2. Reuse of existing SPF/DKIM records
      SPF and DKIM records are DNS-based and are configured once for the custom domain. The documentation states that after verifying sender authentication configurations, “your email domain is ready to send emails using the custom domain.” Any ECS resource that is connected to this verified domain uses those same DNS records; there is no separate SPF/DKIM set per ECS resource.
    3. Recommended way to share one custom domain across ECS resources
      • Provision and verify the custom domain once in Email Communication Services (ownership TXT + SPF + DKIM).
      • Connect that verified domain to an Email Communication Service resource as needed.
      • To use the same domain with a different ECS resource, disconnect it from the first and connect it to the second: “To switch from one verified domain to other, you need to disconnect the domain and connect a different domain.”
        The model is one verified domain linked to one ECS resource at a time; sharing is done by switching the linkage, not by duplicating the domain.
    4. Known limitations / best practices
      • One domain per ECS resource at a time: Each ECS resource is linked with one verified domain; switching requires disconnecting and reconnecting.
      • Centralize domain management: Manage DNS (SPF, DKIM) and verification once at the domain level, then use the connect/disconnect mechanism to move the domain between ECS resources as needed.
      • Service limits apply per domain: Both Azure managed and custom domains are subject to email service limits; plan sending volume and quota requests accordingly.

    References:

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