[SOLVED] Mail server problems

Hello wcat! Thanks for your response.

I've been trying some workarounds and I've managed to solve both issues.

The IMAP test didn't work on 993 port because dovecot ssl config was not set up
/etc/dovecot/conf.d/10-ssl.conf
Dovecot was not listening the 993 port without the proper config file setting up

# SSL/TLS support: yes, no, required. <doc/wiki/SSL.txt>
ssl = yes

Save - Reload dovecot service - port 993 is officially open.

The STARTTLS issue was really hard but the solution was being back to the begining:
I've made a brand new self-Signed SSL certificate

openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/nginx/ssl/newmail.key -out /etc/nginx/ssl/newmail.crt

Then get that certicate to work in
/etc/postfix/main.cf
/etc/dovecot/conf.d/10-ssl-conf

And reload-restart both services.
service postfix reload
service postfix restart
service dovecot reload
service dovecot restart

Problems solved! The funny thing is I've followed the mail server set up tutorial step by step and I didn't modify any of that initial (and presumible working) certificate, but I suppose that anything went wrong somehow in the way.

I hope this experience helps to anyone who would find himself in this desperately-wanting-to-die situation.

Regards!
D.