Hi,
i use my domain with SSL enabled and installed by webuzo control panel.
Before TLS STARTLS works for email, after install SSL or afer (as i do today) remove SSL for install a new SSL for same domain TLS STARTTLS stop to work for email so when you connected to Thubird or other software you receve disconnection message if you are using TLS STARTLS
And for that problem i must learn in the past how to regenerate different new self signed certificate and change for Exim and Dovecot.
So if now I'M using a selfsinged certificate for mail.mydomain.ext wy if i change, remove or install new SSL certificate for mydomain.ext TLS STARTLS stop to work for the selfsigned certificate mail.mydomain.ext.