We are currently aware of a number of users encountering errors with Mail Clients and Browsers being unable to verify the server identity.
To resolve this issue, you will need to reissue the SSL certificate as per the guide below:
https://www.channelislandhosting.net/knowledgebase/7083/Reissue-your-SSL-certificate-using-cPanel-SSLorTLS.html
Once the certificate has been reissued, you will need to restart any devices that have encountered the SSL issue to ensure the device cache is cleared.