How to Fix Actionable Message Signature Validation Error in Outlook
Question details
The user encounters a signature validation failure when attempting to view or interact with actionable emails.
- Product
- Microsoft Outlook / Microsoft 365
- Device & OS
- not provided
- Scenario
- Opening and viewing actionable emails that contain message cards.
- Observed behavior
- Outlook displays the specific error: 'Failed to validate the signature of the actionable message card'.
Confirm whether other colleagues in your organization are experiencing the same issue, as this error typically indicates a widespread server-side problem rather than a local configuration fault.
Submit a Service Request via Microsoft 365 Admin Center
Since this is a server-side authentication issue, it requires intervention from Microsoft engineers through an official service request created by an administrator.
The 'Failed to validate the signature of the actionable message card' error is generally caused by an external server-side problem affecting multiple Microsoft 365 customers. Reinstalling or repairing your local Outlook client will not resolve this issue.
Determine if you have Microsoft 365 administrator privileges. If you are a standard user, you must immediately contact your organization's IT department or administrator to report the issue.
If you are an administrator, open a web browser, navigate to the Microsoft 365 admin center (admin.microsoft.com), and log in using your admin credentials.
On the left-hand navigation pane, locate the 'Support' section and click on 'Help & support'.
Open a new service ticket. Clearly describe that users are receiving the 'Failed to validate the signature of the actionable message card' error when opening actionable emails, and submit the request for Microsoft's technical team to investigate.
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Frequently Asked Questions
What is an actionable message in Outlook?
Actionable messages allow users to quickly complete tasks directly within an email—such as approving workflow requests, filling out surveys, or updating records—using interactive Adaptive Cards without leaving the Outlook client.
Can I fix the signature validation error by clearing my Outlook cache?
No. Clearing the Outlook cache, repairing the data file, or reinstalling the application will not fix this error. It is caused by a server-side authentication failure on Microsoft's end.
How long does it typically take for this server error to be resolved?
Resolution time varies based on the underlying server issue. Once your Microsoft 365 administrator submits a service request, they can track the ticket's progress and expected resolution timeline directly in the Microsoft 365 admin center.
