Why does Outlook Certificate Error occur?
There are a few reasons why the Outlook Certificate Error may occur. One reason may be that the root certificate that is needed to validate the SSL certificate is not installed on the computer. It is possible that the certificate has expired, or that the name on the certificate does not match the name of the site. Another reason may be that the intermediate certificate (or chain certificate) is not installed. It is also possible that the certificate is self-signed.