TLS between MTA's?

Hey :) I understand about SSL/TLS connections between client and server, but what about between MTA's? Will cPanel attempt to send via TLS by default to other MTA's? Will Exim in cPanel accept mail and send mail in plain text if the remote MTA doesn't support TLS for some reason? Is non-encrypted delivery common between MTA'S? Are there settings in cPanel to configure this behavior for Exim? Thanks in advance :)