ACS Email custom domain not delivering to Apple/iCloud while Azure-managed domain works

Dawid 20 Reputation points
2026-09-28T11:51:41.6166667+00:00

Azure Communication Services Email custom domain messages are not delivered to Apple/iCloud recipients, while the Azure-managed domain works correctly.

Custom domain: email.<mydomain>.pl

Reproduction:

  • Azure-managed ACS domain -> same @icloud.com recipient -> delivered successfully
  • Verified custom domain email.<mydomain>.pl -> same @icloud.com recipient -> not delivered
  • Custom domain email.<mydomain>.pl -> Gmail -> delivered successfully

Affected messages remain in OutForDelivery

No final recipient-level delivery/bounce status is generated

The issue can also be reproduced using the Azure Portal test email functionality, so it does not appear to be related to our application code.

SPF, DKIM1, DKIM2 and DMARC are configured and verified.

This appears similar to previously reported ACS custom-domain -> Apple/iCloud delivery issues.

Could Microsoft confirm whether this is a known ACS Email deliverability issue and advise how I can provide a CorrelationId privately for service-side SMTP telemetry investigation?

Azure Communication Services
0 comments
Answer accepted by question author
TP 163.9K Reputation points Volunteer Moderator
2026-09-28T12:43:39.06+00:00

Hi Dawid,

1. Please make sure the custom email domain you are using in Azure Communication Services (ACS) has MX record.

I don't know specifically how iCloud's email server/security gateway treats lack of MX record, but I do know in general it is considered potential spam signal.

ACS documentation recommends having MX record. I would go a step further and say it is best to not only have MX record, but that it points to valid email server that will receive messages for that domain and the MailFrom addresses (e.g. DoNotReply -at- email.youracsdomain.pl, etc.) you have configured.

Have automation that processes any messages that comes in for Non Delivery Reports, manual unsubscribes, opt-outs, etc. This automation part isn't necessary for trying to solve your immediate issue.

After MX record is in place, please verify it resolves correctly using command similar to below. For example, say your ACS email domain is email.youracsdomain.pl:

nslookup -q=mx email.youracsdomain.pl 8.8.8.8

2. For your DMARC, are you using p=reject ? I suspect some subset of servers/gateways prefer p=reject (this is what ACS managed domain is set to) or p=quarantine. Of course make sure the email address you put in your DMARC is real and receives messages.

After performing the above, please test sending to the iCloud recipient again.

IMPORTANT: Azure Communication Services Email (ACS Email) is being RETIRED on September 30, 2028.

Retirement and breaking changes guide for Azure Communication Services - ACS Email

https://learn.microsoft.com/en-us/azure/communication-services/acs-retirement-and-breaking-changes-guide#acs-email

Thanks.

-TP

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