Hello Hakabe!
I've just come trough a painful way to get my mail server working (http://community.rtcamp.com/t/solved-mail-server-problems/8466)
You're going to need a ssl certificate. You can create your own certificate hereopenssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/nginx/ssl/newmail.key -out /etc/nginx/ssl/newmail.crt
Let's keep secure the key filechmod 640 /etc/nginx/ssl/newmail.keychown root:ssl-cert /etc/nginx/ssl/newmail.key
You have to enable the dovecot SSL option here/etc/dovecot/conf.d/10-ssl-conf
And let postfix know about your SSL certificate here/etc/postfix/main.cf
Once you got everything set up, restart/reload the servicesservice postfix reloadservice postfix restartservice dovecot reloadservice dovecot restart
And you finally get your SSL set up ready to secure your mails.
Hope it helps Regards.
D.