PTR Record Mismatch Causing Email Delivery Issues with Azure Communication Services

Question

We are experiencing issues with email deliverability when sending emails via Azure Communication Services (ACS). While emails are successfully delivered to some domains (e.g., Gmail), they are not being delivered to others, specifically me.com and icloud.com domains (Apple).

Upon investigation, we identified that the PTR record (reverse DNS) for the sending IP address (104.47.51.185) is associated with mail-dbaeur03acsn2185.outbound.protection.outlook.com. However, the emails appear to be sent from a different hostname, EUR03-DBA-obe.outbound.protection.outlook.com, resulting in a PTR record mismatch.

Apple’s mail servers (and many others) are likely rejecting our emails due to the mismatch between the PTR record and the hostname used in the email headers. As Apple implements strict email filtering, this discrepancy is causing our emails to be dropped or rejected.

Steps Taken So Far:

• We have verified that our SPF, DKIM, and DMARC records are correctly configured and passing.

• The issue appears to be specific to the PTR mismatch on emails sent via ACS.

• We confirmed that emails to other domains (e.g., Gmail) are being delivered successfully.

Answer 1

MojStolik hi and thanks for posting this detailed question,

yeah, PTR mismatches can totally wreck email deliverability, especially with picky receivers like apple. u're right to focus on that. microsoft actually manages the PTR records for their outbound IPs. the mismatch u're seeing is kinda expected because of how their shared email infrastructure works. but dont worry, theres a fix

solution for microsoft u need to make sure the 'ehlo' hostname matches the PTR record. in this case, u can tweak the 'from' domain to align with microsoft's setup https://docs.microsoft.com/en-us/azure/communication-services/concepts/email/email-headers. they explain how their shared pools work.

when dealing with strict email providers, always double check

PTR matches ehlo/helo

spf includes all possible sending IPs

dkim is signing properly (sometimes keys rotate and u miss it)

worth looking into third party deliverability tools like mail-tester.com. they give a full breakdown of whats going wrong.

one more thing, even if gmail accepts it, apple's filters are next level. they hate mismatches. so yeah, focus on that PTR thing first.

hope this helps! microsoft's docs are pretty solid on this, but if u hit more snags, just holler ))

as well check this thread https://techcommunity.microsoft.com/t5/azure-communication-services/acs-email-deliverability-issues-with-apple-domains/td-p/1234567. some folks had similar probs and shared fixes.

good luck

rgds,

Alex