If you are providing a universal SSL to your mail server, you will need to install an SSL and of course properly link it from your Dovecot configuration file.
This is not a guide how to achieve above but more of what to do after you have successfully installed an SSL. Your Dovecot will hang on to the old SSL certificate until your restart it. Last step people seem to forget and spend endless hours trying to figure out what went wrong in regards to installation or renewal of the SSL certificate. But really all Dovecot needs is a restart.
Service dovecot restart
That’s it!. You will notice your new SSL actually kick in and start to work again.