self signed certs and dovecot imaps : howto? tlsv1 alert unknown ca

How do you setup dovecot to use a self signed cert? One server will be connected to the internet. One will be totally internal and have no runtime access to the internet. Getting the below error msg. Also, I think I have a TLS 1.0 and need a 1.2 cert?...

Thank you.

Jul 28 20:09:27 host dovecot: imap-login:: user=<>, rip=10...., lip=10...., TLS: SSL_read() failed: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca: SSL alert number 48, session=<kK2aELspLpkKAQF5>