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Dynamics 365 on-premise workflow email account not sending emails - Acquiring ACS token Fail

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Posted on by jdalske

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I have an issue where a workflow that was running for 10 years to send an email on lead create (another to send on opp won or lost) stopped working. No errors. These emails come from the same administrative account. Additional workflows have been added using the same account and they do not work either. However, I can send an email from within CRM activities with my user account and it goes through. It appears to be isolated to this one mailbox. I have checked to verify the mailbox is enabled, tested, but it consistently fails. It "broke" around 8/5-8/6 which is the first time I saw the Acquiring ACS token Fail: Please check if your tenantId is specified correctly error in the Alerts. I did verify the tenantid.

I've tried everything from Deactivating, Approve Email, Test & Enable Mailbox but the configuration results remain Failures. This is isolated to this mailbox only. I reached out to a consultant with no luck since its on-premise. Any assistance would be greatly appreciated. Thank you.

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ManoVerse 1,145 Super User 2026 Season 1 on at

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are you currently using Exchange Online or SMTP for your email integration? Also, could you confirm the authentication method configured in your Email Server Profile? If it's still using ACS (Access Control Service), that could be the root cause of the issue you might switch to OAuth.
Microsoft officially deprecated ACS, and while it was announced some time ago, it might enforcement in your environment around in August , which aligns with when your workflows stopped working and the “Acquiring ACS token failed” error began.

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jdalske 547 on at

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@Manoj Chauhan I will take a look and post back. I do know that we had to enable OAuth to get the app for Outlook to work. My main question is why would this break only on one account (our main sys admin account).

We use Exchange Online (Hybrid) for email integration. The owner of this profile is this particular admin. I will check with my network engineer about ACS.

Thank you!

@Manoj Chauhan Update, I looked closer and it appears there are more errors. Although my mailbox shows incoming and outgoing status as success it is throwing the same error in the Alert under the email server profile within CRM.

How do I check if we are still using the deprecated ACS?

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TV-31101437-0 on at

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I'm also wondering how to check if my PRD dynamics environment is still using ACS.

Can you tell how to check this?

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