How to resolve error "Microsoft Outlook cannot sign or encrypt this message" when sending encrypted email?

Overview

The preferred Microsoft Message Encryption functionality does not rely on local client certificates. If you attempt to send an email message, and see an Invalid Certificate error, it may be attempting to encrypt the message using local S/MIME settings and certificates.

 

Error Message

Microsoft Outlook error dialog showing the Invalid Certificate message when sending an encrypted message

Invalid Certificate
Microsoft Outlook cannot sign or encrypt this message because there are no certificates which can be used to send from this email address 'jvandal@uidaho.edu'. Either get a new digital ID to use with this account, or use the Accounts button to send the message using an account that you have certificates for.

 

Outlook on the web

Try to send the encrypted email using Outlook on the web at https://mail.uidaho.edu/.

 

Outlook (classic)

In Outlook (classic), go to the top left File menu and then click on the bottom right "Options".

Outlook File menu with the Options link in the bottom left

Outlook Options dialog with the Trust Center option in the left pane

Click on Trust Center and then Trust Center Settings...

Trust Center dialog with the Trust Center Settings button

Select "Email Security" and verify the options to encrypt and sign are UNCHECKED. Click OK to exit through all of the dialogs.

Email Security settings tab in Trust Center Settings, showing the sign and encrypt options unchecked

Try sending the encrypted email again using the instructions in How to send an encrypted email message.

 

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