Generate the keys in the directory /etc/mail/certs, see New SSL-Key.
Fix permission with:
cd /etc/mail/certs chgrp mail * chmod 640 *
Edit /usr/local/etc/exim/configure:
tls_certificate = /etc/mail/certs/newcert.pem tls_privatekey = /etc/mail/certs/req.pem tls_verify_certificates = /etc/mail/certs/ tls_advertise_hosts = * begin acl
Restart Exim with:
/usr/local/etc/rc.d/exim restart