Invalid Certificate warning when dismissing meeting reminders

Question

every time I open outlook I get several Invalid Certificate warning, the same happens when I dismiss meeting reminders

The certificated are valid though....

Answer 1

Hi @Geormaneanu Antoniu

Welcome to our forum!

To better assist you to solve the problem, could you please describe more about the error?

1. Does the issue occur recently on Outlook Desktop Client? Do you have any specific operation before the issue occurred? 
2. What is the version of your Outlook? It is recommended that you please check the Outlook client version (File>Office Account>Product Information) and try to upgrade to the latest version to see if the problem is resolved. 
3. Would you please provide a screenshot of the error?  (In order to avoid privacy leakage, please remember to hide your personal information.） 

In addition, here are some steps you may take:

1. Check Security Settings:
   • Go to Outlook>File > Options > Trust Center > Trust Center Settings > Email Security.
   • Ensure that the options for "Encrypt contents and attachments for outgoing messages" and "Add digital signatures to outgoing messages" are unchecked.
2. Verify Certificate Details:
   • Go to Control Panel>Network and Internet>Internet Options>Select Content tab, click on Certificates button>Under Personal tab, Select the certificate you applied for and issued to your current account.
   • Please check its valid time and make sure the address it issued to fully match your current account address
3. Clean Reminders:
   • Press Windows key + R to open the Run dialog.
   • Type outlook /cleanreminders and press OK. This can help clear any corrupted reminders.
4. Reconfigure Account:
   • Sometimes reconfiguring your email account can help. Go to File > Account Settings > Account Settings.
   • Select your account and click Remove. Then, add it back again.

Hope it helps! 

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Answer 2

Which Outlook version are you using?

Ensure that Outlook client latest updated. If the Outlook client is not latest updated, check for Office updates and install any required updates.

You may try using Outlook in safe mode and disable add-ins to check this issue.

To start Outlook in safe mode.

1. Choose Start > Run.
2. Type Outlook /safe, and choose OK.

Moreover, use the Microsoft Support and Recovery Assistant (SaRA) tool that can diagnose the Outlook problems. See https://support.microsoft.com/en-us/office/about-the-microsoft-support-and-recovery-assistant-e90bb691-c2a7-4697-a94f-88836856c72f#ID0ED6=Outlook