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I setup DKIM for my domains in MS Exchange 365 on-premise. It worked properly for a long time but recently I found out some of my mails are sent to the receivers spambox as my mails are no longer signed.

authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=mydomain.com;

I don't find any reason why my messages are not signed anymore. I know that messages sent internally, from MS exchange to other MS exchange of the same tenant are not signed on purpose, so I tried with a 3rd party email and online tools to test DKIM - my outbound messages are not signed.

sign messages for this domain with DKIM signatures. Status: Enabled

My DNS, my keys, my selectors, everything is working, even according to MS diagnostics, everything is setup properly.

And even according to MS support, they cannot find the issue:

I also ran several diagnostics on your tenant in regards to DKIM, it is also showing that is working properly.

Does anyone experience the same problem or could help me find out more?

Robotnik
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Daniel W.
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2 Answers2

1

There was a security problem in Microsoft global Exchange infrastructure that disabled DKIM signing without notification several months ago.

I noticed the problem first around September 2022 when my outgoing mails were moved to spam on the receiving site.

Microsoft has resolved this issue in November 2022 and are still monitoring.

Daniel W.
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0

I want to confirm if you send all external mails are marked as spam or only send to the specific recipient that the mails are marked as spam?

Does the issue occur to use both OWA and outlook send mails?

Could you try to reconfigure DKIM via following the guidance and check if the issue continues?

Joy Zhang
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