Port 993 closed and impossible to open

I started using Ajenti V Mail, but when installing a RainLoop it says:

Using SSL/TLS

stream_socket_client(): unable to connect to ssl://mydomain.tld:993 (Connection refused)

Using STARTTLS

stream_socket_client(): unable to connect to tcp://mydomain.tld:993 (Connection refused)

I added a rule to the firewall and nothing. Also via command line with iptables. The rule is:

--protocol tcp -j ACCEPT --destination-port 993 --match tcp

I have a valid SSL certificate, the TLS setting is enabled and configured. Also the SMTP SSL/TLS port is open and I don't have a problem with it.

Thanks.