Many a time, having a simple name mismatch in the domain name causes Outlook to believe that the certificate isn’t secure.
That message is saying that the certificate the mail server uses has likely expired. This hard to understand error means the security certificate your email server is using has expired or is invalid for other reasons. When I open Outlook I get a certificate error? Open Account Settings in Outlook and click on the advanced tab. This error is caused by a mismatch when enabling SSL and your port number in your account settings. Troubleshooting the Outlook 2010 error: Security Certificate cannot be verified. How do I fix certificate errors in Outlook 2010?
