This might help: https://support.google.com/mail/answer/21291?hl=en https://support.google.com/mail/answer/21291?hl=en What are the SSL certificate authority r

This might help: https://support.google.com/mail/answer/21291?hl=en https://support.google.com/mail/answer/21291?hl=en What are the SSL certificate authority requirements? We do not accept self-signed certificates. For a certificate to be valid it needs to chain up to a valid CA, like one in the Mozilla CA list.