This might help: https://support.google.com/mail/answer/21291?hl=en *What are th...

		tantalor on Feb 9, 2016 \| parent \| context \| favorite \| on: Gmail Will Warn If Message Is Not Authenticated/En... This might help: 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.

That's obviously for mail retrieval, so doesn't apply here.