Azure Communications suddenly fails to deliver to Gmail due to not being RFC 5322 compliant.

Frooxius 50 Reputation points
2024-08-06T01:03:03.7033333+00:00

We are using Azure Communication Service to send emails to our users. We have noticed that within last ~7 hours, emails suddenly fail to deliver to Gmail addresses.

We have not made any changes to our server code or to our Azure setup.

Analyzing the logs on Azure, majority of failed deliveries have following properties:

SmtpStatusCode: 550

EnhancedSmtpStatusCode: 5.7.1

FailureReason: DeliveryNotAuthorizedMessageRefused

FailureMessage: This message is not RFC 5322 compliant. There are multiple Message-ID 550-5.7.1 headers. To reduce the amount of spam sent to Gmail, this message has 550-5.7.1 been blocked. For more information, go to 550-5.7.1 https://support.google.com/mail/?p=RfcMessageNonCompliant and review 550 5.7.1 RFC 5322 spe'

I have used the "Try Email" functionality in Azure portal to send a few test messages. Those fail with the same exact properties as above. This suggests to me that the issue is not due to our code.

Does anyone know what could've caused those errors all of sudden? Is there any way to resolve these?

Azure Communication Services
Azure Communication Services
An Azure communication platform for deploying applications across devices and platforms.
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