Outlook Error: Invalid Certificate

When troubleshooting Outlook, it is good to note any error messages. The error "Invalid Certificate: Microsoft Outlook cannot sign or encrypt this message because there are no certificates which can be used to send..." occurs when attempting to send a regular unencrypted message from the Outlook desktop application, if the Trust Center Settings are set incorrectly. This can happen when upgrading Outlook or when Windows updates change the Trust Center Settings.

Send It Secure adds one-click, HIPAA- and GLBA-compliant email encryption right inside Outlook (classic) on Windows — send secure messages without ever leaving your inbox. The quick fix below clears the "Invalid Certificate" error so your add-in keeps working smoothly. Learn more about Send It Secure by Protected Trust.

Hint: Remember you can always go to https://app.protectedtrust.com and sign in to the web app to view protected messages in your Inbox or Compose and Send a protected message.

Steps to resolve the Outlook Add-in error "Invalid Certificate: Microsoft Outlook cannot sign or encrypt this message because there are no certificates which can be used to send..."

  1. If you receive the error, "Invalid Certificate", in Outlook, on the File tab, select Options Invalid Certificate error in Outlook
  2. Click Trust Center, and then click Trust Center Settings Trust Center Settings
  3. Uncheck the option to Encrypt contents and attachments for outgoing messages, remember to click the OK button to save Email Security settings with Encrypt contents option unchecked
  4. You should now be able to send regular unencrypted messages when the lock is unlocked, and encrypted secure messages when the lock is locked Message lock icon in the Outlook Add-in