PTR Record Mismatch Causing Email Delivery Issues with Azure Communication Services

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.