unable establish remote imap connection, why not?

A remote CentOS 7 web server is able to successfully receive email sent from elsewhere on the internet addressed to me@mydomain.com . An app running on the same CentOS 7 server is able to use JavaMail to make an IMAP connection to the dovecot Maildir where the incoming messages get stored. So what do I have to add in order to for Thunderbird running on my devbox to be able to make an IMAP connection to the remote CentOS 7 server across the internet?

So far, I added imaps to the public zone of firewalld. I also confirmed that dovecot.conf contains the line protocols = imap pop3. I configure Thunderbird to use IMAP for incoming mail, with mydomain.com as the hostname, with port 993 and SSL with normal password. And I confirmed at my domain registrar's web site that the dns mx entry uses mydomain.com as the mx address.

What else do I have to configure?