This issue occurs in Outlook 2016 for Mac version 15.9 and later versions when Outlook performs an Autodiscover operation and tries to connect to a service endpoint whose expected name is not present on the server's Secure Sockets Layer (SSL) certificate. However, the warning may reappear the next time that Autodiscover runs. When you receive this warning message, you can click Continue to accept the warning. If you continue, the information that you view and send will be encrypted, but will not be secure.
A secure connection cannot be established with the server because its intermediate or root certificate cannot be found.
